Setting issues on Diplomat APM 6855 fridge freezer?

I have the above fridge freezer and tried to lower the fridge setting from +6 to +4 degC using buttons. Appear to have messed up settings so now cannot change temp which remains on horizontal line -
Light gone off so fridge seems to be in STOP mode referred to in manual and is not cooling. Manual does not tell me how to get out of STOP and is pretty unhelpful.
Freezer is working well.