If it is just stuck on the rack, it might be easiest to just replace the rack.

If it is on the bottom, have you tried to just scrape it off with a spatula? Or heat it back up a little and carefully scrape it (I would wear those long fireplace gloves and a putty knife.

If you have a home cleaning service they might be able to do it?

Oh gosh, no real advice, but that sucks!

I often leave my cast iron skillet in the oven and DH has turned on the oven so many times without realizing. At least you can still deal with a red hot cast iron, not so much the plastic!

I hope you can find something that helps.

We turned the oven on forgetting that there was a ton of plastic containers in there from the holidays. It's all melted inside. Any suggestions on how to address this? Any professionals?