Set to coarse. If that does not help, then you have to disassemble it.

I had the same problem because a plastic part broke off the grinder thickness adjuster and jammed the grinder.
Disconnect the power, dismantle until you can see the grinder and the part from above. Heat the plastic part with a lighter (the grinder is made of metal, so it doesn't matter), switch on the power and let it grind: the part is gone.