What type of heads do the screws holding the cover on the chuck end of my drill. I can't see down the holes

If you look at the end of the shaft on the drill after it unscrews, there will be a hole with threads inside--if not the screw may have broken off---your missing screw that holds the chuck on--it's a left handed threaded screw---it's head may be slotted--philips---torx---or allen---this is available at your Dewalt dealer or tool repair---all that needed is the size/model number of unit---screw the chuck back on tightly then open chuck jaws all the way then put the holding screw in---tighten it down---REMEMBER IT'S LEFT HANDED----GL

If it is a reversible drill there is almost certainly a left-handed thread screw or allen bolt through the centre of the chuck into the drill shaft and this must be removed before the chuck can be removed.

If it is a keyed chuck select low gear if there is one, fit the chuck key and then strike it sharply with a hammer to jar the chuck in an anti-clockwise direction. Usually it takes only a couple of blows before the chuck is loosened.

Keyless chucks are more problematic. I hold them in a vice and use the drill in reverse which has proved fairly successful, though sometimes the chuck is only fit for scrap afterwards.

Lots of the keyed chucks can be taken apart for cleaning and lubricating if necessary.

I am assuming you are reffering to the torque setting on the transmission that is set by turning the numbered ring just behind the chuck on the drill. The ring adjusts the torque where the motor will not be able to turn the chuck any more. At the lowest setting, 1 or 2, you can hold the chuck with your hand and the motor should turn without turning the chuck in your hand. This setting would let you turn screws into threaded holes or nuts but not let you over torque them and strip out the threads. Higher settings will let you drive screws into wood to a determined depth like flush with the surface or slightly countersunk. This depth will also be affected by the hardness of the wood so if you hit a knot the depth will change. The highest settings will drive screws or bolts in very tight before the transmission will slip.

try to jam the chuck so its open. Put the forward and reverse so that it is slipping (like a grinding gear sound) and hold the drill upside down. If that doesn't work ,buy a screw extractor kit.

Open the jaws of the chuck all the way open. Inside the chuck you will see a slotted screw. Use a large flat head screw driver and remove screw. It will have left handed threads.

After you remove the screw put the end of the chuck in a vise where the 6 flats sides are. Put the drill in low gear and reverse. Hold tight and turn on the drill. This should run the chuck right off the spindle.

Drill a hole in the top of the phillips head screw with a 3/16 th's bit. Don't drill the head of the screw off, just drill deep enough for a torx bit to hold. Take a T-30 torx bit and tap in into the hole you have drilled. Then turn the screw clockwise and it should come out fairly easily.

Place drill in vice with chuck in vice facing up . Clamp chuck lightly but with enough force to hold firmly.
put allen wrench in chuck and lightly tap down to make good fit to allen screw head.Clamp chuck jaws down onto allen wrench lightly to hold wrench steady. Take piece of pipe to end of wrench,10".
These chuck screws are tight. Hammer clockwise until screw brakes loose.Open chuck completely and remove screw.Chuck is threaded to spindle shaft . Place allen wrench with long end facing out of tool in chuck and tighten chuck securely. With hammer tap allen wrench sharply counter clockwise ( normal thread.)

Grasp chuck, reverse it until fully open. Look inside where bit goes and should be an allen head or torque head screw holding chuck to motor arbor/shaft.

I had the locking screw come loose in the center and bottom of the chuck it has a left hand thread and is a torx head . It had backed out and prevented the chuck from closing.

To remove the chuck on your drill follow the instructions for the type of drill chuck you have:
Instructions for removing a keyed chuck
Most reversing drills have a left hand threaded screw located inside the bottom of the chuck.
1.) If the unit has this screw place the chuck key, with the chuck facing toward you, into one of the holes on the right side of the chuck. Strike the key in a clockwise direction with a wooden mallet or similar object. This will loosen the screw inside the chuck.
2.) Open chuck jaws fully. Insert screwdriver into the bottom of the chuck to engage screw head. Remove screw by turning clockwise this is a left-hand screw.
3.) With the chuck facing toward you place the key into one of the holes on the left side of the chuck. Using a wooden mallet or similar object, strike the key sharply in a counter-clockwise direction. This will loosen the chuck so that it may be unscrewed by hand.
There is no way to stop the motor from turning.
It may require several attempts to loosen the chuck
Instructions for removing a keyless chuck
Most reversing drills have a left hand threaded screw located inside the bottom of the chuck.
1.) If the unit has this screw open chuck jaws fully. Insert screwdriver into the bottom of the chuck to engage screw head. Remove screw by turning clockwise this is a left-hand screw.
2.) Insert the short end of a 1/4" or larger hex Allen wrench into the chuck and tighten. Facing the tool strike the long end of the hex wrench sharply counter clockwise as it is a standard right hand thread. This will loosen the chuck so that it may be unscrewed by hand.
There is no way to stop the motor from turning.
It may require several attempts to loosen the chuck