My camera has a broken diopter

My camera has a broken diopter, when I turn the knob it does nothing to my viewfinder focus. Could you post a guide on how to fix that? I would also need a part, not sure where to obtain that...

crwdns2934089:0crwdne2934089:0 crwdns2934093:0crwdne2934093:0

crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 1
crwdns2934285:0crwdne2934285:0