Can I get into the trunk from inside my car? How does the back seat fold down?

https://my.buick.com/content/dam/gmownercenter/gmna/dynamic/manuals/1996/buick/regal/1996_buick_regal_owners.pdf That's the owners manual for this vehicle - refer to it for any operational questions. From what I could tell, I do not see any indication that the rear seats of this vehicle fold down. I do not believe you can get inside the tank from inside the car, see a local locksmith near you for assistance.

While looking in the owner’s manual check out jump starting - should have remote jump start terminals under hood - connect jumper cables - unlock trunk using release button.