Assuming you have the door panels off you can just push the staples through the felts and bend them back with a small screwdriver. Some people use pop rivets. Either way will work. It depends on how you want it to look. Good luck.
I painted the staples before I installed them on my XR7 as the supplied staples are shiny and will be forever an eyesore. The original staples were painted. I used a small pair of slip-joint pliers and taped the ends of the pliers with electrical tape to prevent damage to the painted staples or leave marks on the felts. I then held the fuzzies tight to the trim and bent the staple ends slightly towards each other , then clinched the staples closed with the pliers. They look as original.
I also used pliers after drilling holes in the right spots.I didn't bother w/paint or tape.Staples are the way to go for the original look however I never noticed any paint on the orgs I removed.Rivets or screws work but incorrect.
I have found a simple way to do this. First remove the old felt, compare it w/ the new one. Align the new one on the door panel. Using a small "needle nose / long nose" Vice grip Part#6LN, clamp the piece in place. Drill the first set of holes, starting in the center. Push the first staple thru the holes. Take the vice grip, fold the lip outward and clamp the staple in place. Take a small hammer or other tool and bend the staple tips toward each other. Now undo the vice grips and use the vice grips to bend them down. It works great and takes just seconds per staple.