So welcome Ann Marie! If you ever go camping, you can toss glass bottles in the camp fire. You will have to have someone "man the fire" all night as you need to let it cool down naturally. Do not toss water on the fire or you will shatter the glass. Remove 24 hours later with tongs carefully. Ours never turned out Pinterest worthy.
Hi. Glass becomes pliable at around 1200 -1250 degrees Fahrenheit. It needs to be done in a kiln.
I found an article that might help you - https://www.craftsuprint.com/projects/crafts/various/how-to-flatten-glass-bottles.cfm
I hope it helps, good luck!