See this link: http://askruth.blogspot.com/2006/07/cleaning-baked-on-foil-in-oven-help.html
"I called Sears and this is what they said to do:
remove as much of the foil as possible Turn oven on to 200 lay an old
wet bath towel on top. Use a plastic spatular to remove the foil.
said it will take some time to remove the foil, in some cases days, and
that you can still use the oven but DO NOT use the self cleaning untill
all the foil is removed."
If you can remove the bottom drip tray/pan from your oven which the
tinfoil is stuck to, than remove it. Ovens with "hidden element"
usually have the removable bottom tray/pan. Don't scrape yet!!
Lay the tinfoil laden tray on a flat service where it wont be disturbed for a couple of days.
Now remove any tinfoil you can with a plastic scraper/spatula/pancake flipper.
Once thats done, pour bleach directly onto the drip tray/pan until it
covers all the stuck tinfoil.(assuming your oven pan is like mine and
has a lip all the way around and is somewhat countersunk).
the bleach in for about 2 days. Now get your plastic scraper again and
scrape away. The stuck tinfoil should all be dissolved by the bleach
and the scraper should get rid of any residue. Then rinse!
method will probably leave some darkened stains on the oven tray, but
not near as ugly or noticeable as that melted tinfoil!!