Yikes! Tin foil on oven bottom completely stuck. See photo.

Take paper towels, lay over the foil, dribble vinegar on the towels until they are soaked. Let sit for an hour or so. Should be able to wipe up after that. Someone did that in my oven too - they didn't know better - you live and learn! Vinegar can fix almost anything! ☺

try to scrape it off with a pallet knife after leaving it to soak in soapy water.

Pull up as much of the foil as you can. Then around the edges soak with hot soapy water....do it little by little and should come up. Vinegar may help also but try either one. I am sure this has happened to a lot of people.

Try heating the oven up and then let it start to cool down to soften the gook that is stuck. Use a plastic spatula to scrape as much off as you can.

when all is clean on the oven bottom, there fiberglass “splat mats” got a set from the worlds largest on line realter...any thing burnt just slides off. well worth getting a set.looks like the price runs 11 to 17 usd. Oven liner is what the big A calls them.

If the oven is self clean, usually it is not recommended to use foil at the bottom. If you do feel it is necessary, use the thickest, best brand name that you can find, and fold the edges up and over a little all around, to simulate an edged cookie sheet. That way, the foil will be able to catch any spills. If the foil does get gunked, then remove asap, and replace. Cheap priced foil is thin, tears easily, and is not as strong as better brand names.

I have a self cleaning (electric) oven that I use a non-stick oven liner to catch spills. However, it should be removed if you are going to use the self-cleaning feature. This wipes clean easily with a soapy cloth. After you get the foil out, I recommend:

https://www.ebay.com/itm/Non-Stick-Oven-Liner-Large-Reusable-Dishwasher-Safe-Teflon-Baking-Spill-Mat-NEW/191717215681?epid=691400295&hash=item2ca33c8dc1:g:4BkAAOSw23NZlzpG