We went off grid for the first time a couple of weeks ago and had same problem. Also our marks on the knobs have now worn off. If same as ours, the knob needs to be pointing just after the '12 o clock' but before '1'. If too cold turn back to '10 o clock'. Ours doesn't seem to have any control between these numbers. We also have a thermometer on a wire so we can keep a check of the fridge. We found just opening it for a few seconds the temp could climb 6-7 degrees but took 4 hours to get back. Maybe google ' instructions for ....fridge' , that's how we found out about ours. Sorry all paperwork is in fridge at mo and too dark to go and find!.
Good luck, Chris