Barb L. - the OP said it was the interior metal/electrical part that is food-encrusted. You absolutely CANNOT fill that with hot water & dish soap & soak. What you're advising the OP does just invites ruining the unit or electricution.
Watermelonman - I'd do two things before trying to resolve this yourself. First, I'd see if the cooker manual has anything about what to do if this happens (although you've probably done this). Second, I'd do an online search for the company that made the cooker, see if that has any info, & if not, contact them & ask for advice.
One thing I'd definitely do is stop trying to scrub it off until you get advice from the company. You could be doing more damage than just the unsightliness of the cooked-on food.