Unplug disposal and and then you might be able too reach it. If it is jammed, there is an Allen head bolt on the bottom of the Disposal. Turn it in either direction and it should free up. Again, make sure the disposal is unplugged.
I would recommend a plumber to handle this situation but if you feel you can do this yourself then, I would recommend that you unplug the disposal and take it off the sink. That way it will be easier to reach and see where the problem lies.
Disconnect power to the unit. Then grab a small flashlight and look in there to locate the piece of metal. You can use a telescoping magnet to get metal items that are not stuck. They sell them at any hardware store. However, if it is stuck, then you will need long bent-tip needle-nose pliers, also available at any hardware store. Best tool I’ve ever owned for retrieving items out of a disposer. Once you get the item out, you may want to try to turn it from inside with the pliers to make sure the blades can move freely. If they won’t move, then try using an Allen wrench on the bottom of the motor in the cabinet to free it up. The Allen wrench that came with your disposer is probably in a drawer or cabinet near the sink, and you probably always wondered what in the heck it was. Once freely moving, then, reconnect power, and if necessary, you may need to push the reset button on bottom of the unit. That should take care of it. If it is still running a bit rough, try putting some ice, a lemon wedge, and a bit of vinegar and olive oil in there and running it. Disposers are like boats…the more you use them, the less they break down.