If you are brave at heart (not really difficult) do a google search and check the procedure.
The lens and body "key" most likely got misaligned although the only time I've seen it happen is when removing/installing a lens.

You need a screwdriver to come in from the rear with the film back removed.
The only real danger is if you slip off the slotted key with the screwdriver and scratch the rear element of the lovely Zeiss you have mounted.
There is a tool made for this purpose but a screwdriver works with care.