How can I open petrol cap on corsa if central locking is not working?

The central locking to open my doors on my corsa is not working meaning the petrol cap will not open. Is there a way you can get the petrol cap open without the central locking as I am a bit short of money at the moment and probably cannot afford to get it fixed.

The doors are locking when I press the button but will not open.

Please help.

Thanks