First of all you’ll want to unplug the disposal or turn off the power for safety purposes. Once that is complete, if there is a humming sound but no movement you’ll want to get an Allen wrench and put it in the bottom of the disposal you can try to turn it back and forth about a half turn and then plug it in and see if that freed it up.

If there is no noise, make sure the device has power. It could be connected to a GFCI that needs to be reset or a breaker could be tripped.