HEEELP How to remove yellow burn stains from microwave cabin?

If it doesn't come off with a normal "spay 'n wipe" type of thing, then just leave it. Who is worried about a stain on the inside of a microwave?

I would use Soft Scrub with bleach and let it sit for awhile before rubbing and rinsing. 

Whitening toothpaste might work. Rinse well after scrubbing.

I would consider trying to use some cleaner intended for glass cooktops. They are a very fine abrasive.  Don't use an abrasive cleaner like Comet. It will scratch the finish and make it harder to clean in the future. if none is available a paste of vinegar and baking soda should work. Try very hard not to get any in the ventilation holes though. If you do use a brush to remove it. Blocking them could cause the unit to overheat.

I'd try a magic eraser