Replace the back of a dkny watch after replacing the battery,

For closing your caseback you need the man with very strong hands first, but it might not work as some casebacks can be closed using special tools only.
Before you visit the watchmaker, try this: first of all open your bracelet by taking out spring lug. This will make more space at the back. Then take watch caseback and check for groove in it. Align that groove with stem (pin going into watch movement) and deepen grooved caseback side as it should be. Then without turning caseback apply great pressure with both hands to the watch(from caseback and dial sides). If hands are strong enough, caseback should snap on into place.
In case if it doesn't work, find a piece of thick leather (wide mens belt will do) and place it on completely flat surface (table top). Place the watch face down on that leather, adjust caseback groove with stem again and try to press caseback down with both hands, only this time using your weight.
If all mentioned above doesn't work- you have to go to see watchmaker.

Good luck.

Arthur