The fuel door release lever can be found on the floor to the left of the driver’s seat. It will be marked with a small gas pump icon to indicate what it’s for. When you locate the lever, pull upwards until you hear a small pop. That’s the sound of the gas tank door releasing.
Once you do this, you’ll be able to swing the fuel tank door open from the outside, at which point you’ll be able to unscrew the gas cap and gain access to the gas tank. If your fuel door won’t open, however, it’s time to take a trip to the mechanic.