You don’t need to press a button or pull a lever to open the gas tank door on your 2013 Toyota Avalon—you simply press the right side of the gas tank door, itself, and it’ll pop right open. Note that your vehicle needs to be off and unlocked in order for this to work! If your car is locked, the gas tank door will be, too.
Once you’ve opened the door, remove the gas cap by twisting it counter-clockwise. Fuel up, then replace the cap by twisting it clockwise until it clicks. Then, shut the door by gently pressing it in the same place as before.