The cable release is held on the inside of the bottom centre panel next to the hole where the petrol tank neck comes through (no surprise). There is quite a bit of plastic removal to get to it starting at the rear end. But I think that any adjustment is probably near the ignition key, which is also a pain to get to.
If you want a quick win without removing plastic you could file away a little bit of the tooth when engages with the petrol door lock, but obviously be careful only to take enough off to make opening it a little easier..
My petrol cover door used to be very sticky but seemed to improve after I removed it to get at the valve cover..
See
Valve clearance check - which panels need to be removed?
for some information on Panel removal.
Hope this helps...feel free to come back with questions..