Take the fob apart. Careful not to lose the little steel discs.
Remove all the little switch discs and set them to soak in an alcohol bath to remove any contamination.
Use alcohol to clean the surface of the PC board. If needed, use a pencil eraser to remove any contamination or oxidation.
Wipe off and allow the discs and PC board to thoroughly dry.
Carefully place one little steel concave side down over each used switch target. Note: Many fobs do not have all the switches used.
Place a strip of Scotch Magic Tape to cover all the discs and press down to make sure it adheres to the PC board with all the discs in place.
Trim excess tape from around the PC board.
Assemble the fob. Check each switch to ensure it can be heard operating as you push it. Try the fob.
See: https://www.youtube.com/watch?v=dagH0ZN_2A0
Thank you. Rich Knowles