If they are screwed on you should remove the plastic and will see the screws. If the plastic doesn't seem to be removable they are probably glued on. Use a heat gun. They look like an industrial hair dryer if you're not sure. Carefully warm it up and with a thin putty knife slip it under to remove it. Double sided tape, available at most any automotive parts store, will put it back on. If the plastic has deteriorated you maybe should look to replace.
Roger in NJ
" Democracy is the worst form of government. Except for all the rest"
Winston Churchill 1948
TAC - NJ 18