the gas cover are opened and closed from the air tube coming out of the central locking pump. when i bought my crossfire the central locking system wasnt working and i was in the exact same spot as you. you have to open the trunk and remove some of the covers of the gas side and put in your arm between covering and the bodywork of the car. next to the gas is a level you can pull to manually open.

look at the picture. you need to find the red part by feel:
https://www.crossfireforum.org/forum...chanism-72.jpg