How do you clean burnt spray starch off your iron?

Let the iron cool. Then on a metal pan like a brownie cooking pant that's about 9" by 12" put down a layer of salt. Then work the iron back and forth on the salt and that should take the spray starch off the bottom of the iron. You'll need to rub vigorously but it works well.

I wipe it down with a vinegar water solution, or even use that solution with a toothbrush to scrub it off. It helps if the iron is hot when you wipe it down if it won't work when it is cooled off, you just have to maybe wear an oven mitt or something.

I use salt, just pour some on a paper towel set the iron to just warm and run it across the salt a few times, it keeps my iron clean.

Vinegar

Rub white vinegar with a soft cloth

I use a product called Iron-off by Dritz. You can get it at a store like Joann's. Works really well and quickly.