Shay - Welcome to the boards!
Your best bet is going to be to try to go from the top and not the side. I tried several times to get the side off and I was never successful, I was too afraid that I would break those switches you are talking about. Once you get in from the top, push the knob in and out several times to find the mechanism, make sure to pay attention to everything that's moving and you should be able to troubleshoot where the problem might be. Hit the mechanism with some sewing machine oil since you're there, it could be that something is gummed up. Just whatever you do, don't try to force the knob to turn, you could damage it further.
To me, though, it sounds like maybe a spring or a lever has snapped and if that's the case, your best bet is to take it into a repairman and let them fix it, trying to find second hand parts for this machine can be a migraine inducing episode because there's just not that many left. Most have been scrapped out for the cast iron and aluminum. Even if they don't have the exact part, they may be able to find something that will work.
Send me a private message with your email address and I'll send you a scanned copy of the manual for the machine.
Keeping fingers crossed for you!