No questions or advice beyond " Have you seen your Doctor?"
If they say yes to having seen their Doctor and are are still getting pain I would suggest you advise them to "Go and see your Doctor again and tell him/her what pain/discomfort you are having before you continue any form of indoor cycling or exercise in general!"
For Fitness Instructors that is where the advice should end.
If they come back with a Doctors clearance then you can look at their set up.
If you make an adjustment pre a Doctors clearance and it makes any injury worse, it's you they will come after!
RPM is not going anywhere. It will be there when they get back!
Revs.
No Fluff!
Food is Fuel.