Forgot to add I did crank the atv a couple time fixing other things could that be the reason why it closed up on me because it was open when I took it off
Typically I take one of the old brake pads and place it across the back of the caliper . I leave the other in place , over the piston to protect the piston. Then I use a C-Clamp to force the piston back into the caliper.
It is very important that you dissipate the force of the C-Clamp with something like the old brake pad, or another object. If you fail to do do, you will blow a hole in the piston, or the back of the caliper.
Those pads don’t look extremely low. They probably need replacement now because it looks like you may have cracked the edges by trying to force something in between. Perhaps you were trying to separate the pads with a screwdriver?
Also, I am not sure if your model has a parking brake lock on the hand lever. If it does, verify that it is released before proceeding with your C-Clamp. Then make sure you open the bleeder slightly before you compress the piston.
Bleed the brakes when you are done. That’s a good time to gravity bleed and flush all that old brake fluid out.
There are probably videos that will help on YouTube .