You probably don’t need this any more since it’s been six months since you posted this, but the rear seat upholstery is held on by hog rings. Hog rings are like thick metal staples. You can use wire cutter, end cutter, or small bolt cutter to cut them. But you will need new ones to reinstall the seat cover. You also need a tool called a hog ring pliers. They have cheap ones that are like five dollars and more expensive ones that are closer to $20 it’s worth it to get the $20 pair, the cheap ones will drive you absolutely crazy.
This type is good. After looking at amazon, there are some decent pairs at closer to 10.
Cascade Tools Hog Ring Pliers Kit (200 Pack of 3/4" Galvanized Steel Hog Rings Included) Perfect for Furniture Upholstery, Auto Upholstery, Meat & Sausage Casings, and More! - - Amazon.com
Good luck