To switch hot air heating on (I assume you have this and not the aux ‘hot water’ heater) select the heating icon - squiggly lines on the display (press the knob); next select ‘on’ by pressing the ‘up’ triangle; next rotate knob to right to find temperature adjustment and select up or down accordingly. Note, if the inside temperature is above that showing on the display it won’t operate. Sounds obvious, but I’ve fallen foul of this and thought heating was faulty.
Let me know if you need any more help.