Okay, first thing I’d try would be to run some hot water and turn on the disposal once it backs up into the sink. If that doesn’t do it, I’d pull the trap under the sink (put a bucket under it) and make sure that’s clear. You can also run the sink with the trap off to make sure the disposal drains.
If that’s all clear,I’d make sure it’s not clogged where the pipe goes in the wall as far as I can see (they make plastic, barbed strips you can push in there to check for clogs)
Beyond that, a plumber can snake the drain.
