I have a DeWalt 788 scroll saw, I changed the blade but it keeps coming out of the bottom blade holder and bending blades. What causes this and how do I fix it.

It sounds like a design issue. Contact their Support line and ask if there are any recalls or improvements for blade alignment.

https://www.dewalt.com/product/dw788/20-variable-speed-scroll-saw

Yes, looks like a few issues!

https://www.google.com/search?q=Dewalt+DW788+scroll+saw+blade+clamp+issues

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most scroll saws have pins on the ends of the blade
the end opposite to the motor is a spring so press down on that end and the blade should come out of the holder slots

You've hit something (metal) and knocked the edge off of one side of the blade----replace blade it should be good---GL

Check out the brushes for contact on commutator.

First: if there is looseness in the table, it is dangerous. So I would check all the parts for wear. If, for instance, a knob worked loose, the bolt could have worn (via vibrating) the bracket, resulting in you being unable to tighten it correctly. Occasionally I take mine all apart and check it all over for just that reason. I also check all the knobs just before use to make sure they are all tight. Here is a web page talking about Dewalt scroll saw problems and solutions http://www.scrollsaws.com/SawReviews/DewltTuneUp.htm

I have no idea most folks throw them away.

Part is $84.00 Are the operators crowding the tool, blades sharp? Scroll saws do not cut quickly.
https://www.ereplacementparts.com/dewalt-dw788-type-scroll-saw-parts-c-1009_2631_2632.html

In short, with as little force. 1) use a hex key to remove a small bolt at the tip of the reciprocating blade holder, right at the base of the blade. the blade should now wobble, but you may not be able to pull the blade free. 2), turn the saw so that you are looking from the front, blade pointing right at you. now slide the blade as far to the LEFT as possible. this should be the position that the blade clears the little round retaining nub on the left side of the shaft that fits through the hole on the blade and pulls free. sometimes the blade is too thick or is bend so this is difficult. 3) try yanking or wiggling while the blade is slid as far left as possible. i just had to pry / knock the blade free with a screwdriver and hammer. there is a narrowing at the very base of the blade before it enters into the mounting hole, and i just used a screndriver wedged in there and hit iy with a hammer WHILE having the blade slid over into the left position. 4) to make it easier for yourself the next time, use sandpaper to remove the paint of the base of the new saw blade, so you will be able to easily pull it free.

Email me with pics of your blade holders and explain more on where the blade is bending. pics will help. [email protected]

Ray

Scroll saws generally have to be loosened in two spots. One spot is above the blade near the tip of the arm. The other is generally below the plate. Most scroll saws come with a special tool that has an allen wrench type end accompanied by a round peg that is inserted just above or below the spot for the allen wrench.This peg type end helps to hold the tool in place and keeps the saw arm from moving around. The other end of the tool has a handle.
Hope this helps.