How do we properly clean a tumble dryer?
I would wipe down the inside of the dryer with soapy water to remove any chocolate that could come in contact with your clothes as this should prevent any of your clothes from picking up stains.

As for the chocolate that might have made its way past the drum, there's no easy way to remove this without disassembling the dryer, but I wouldn't really worry about it too much.  If you were to take apart your dryer, you'd likely find all sorts of debris in there.