Seat release knob

There's a slide release and a back release. A few models had the back release high up on the side of the back. You said "cover" so I'll guess that high one is what you have.
Anyway... the knobs ( except headlight switch knob ) that don't have a set screw have a tempered steel piece poked inside that provides a tooth to the steel arm or switch shaft its on. You can poke a tiny tool like dental pick in/around at it to try getting a little release or just pull and hope for the best. Most cases the knob does come off leaving the tempered steel finger bit on the arm or switch shaft.
So now you need to clarify exactly what you have and create a parts wanted ad.