Typically, it is in the trunk, but the manual will give you the specific location. Once you’ve filled up, you’ll have more time to determine if you just have a bad fuel door fuse or if you need the release spring replaced.
If the door is actually stuck or jammed, try sliding a credit card or using a flathead screwdriver to pry open the door while someone else presses the fuel door release button.
If neither of these tactics works, it’s time to head to a mechanic.