If the rubber layer separated from its adhesive pad:

Slide the flat end of a spudger under an edge of the adhesive. If the adhesive seems stuck, you may need to heat it further.

Peel the adhesive off.

To install a new foot:

If any of the feet got damaged during removal or separated from their adhesive pads, replace them.

Use a spudger to carefully scrape up and remove any remaining adhesive bits.

Use isopropyl alcohol and a microfiber cloth to thoroughly clean all adhesive residue from the foot recesses. Allow the surface to completely dry.

Remove the feet from their backing and firmly press them into place.