My TOTAL key does not work (comes off) making other keys scream

My TOTAL key does not work (comes off) making other keys scream

I have a ROYAL 482nx. It has worked great for years. (my daughter used to play store and now my grandkids want to) The TOTAL key doesn’t work it has become loose and can easily lift off) When I push other keys now the register lets out a loud continuous beep. How can I fix the TOTAL key?