You might have to yse a plastic scraper to remove most of it. Try heating it a little first to get it supple and then try.
spray with dawn and water, heat for a few minutes and get a plastic scraper from the auto store and scrape it off.
Here are some videos for you to watch! Good luck to you.
Once you get it clean use an oven liner for the bottom to help this problem in the future.
After using the oven it may help using a metal or flat spatula to pry it up. Being warm may I loosen it. It’s stuck to the sticky drip of whatever it was.
Warm water on a plastic scrubby
A plastic scraper and warm it a little to help loosen it. The suggestion about using the oven liner that is made for the oven is a good one. I always use one and it really helps making the cleaning easier, you just take it out and clean it and put it back in once it is dry.
add some water & dawn dish soap to bottom to cover foil let sit the longer the better plastic spatula,steel wool,SOS or Brillo pad use towel/sponge to absorb the excess water