Ferroli Falcon pressure probs?

Decorating front room, so turned rad in the room down to stop paper drying too fast. This resulted in a leak from the thermostat valve, which my landlord sorted out with PTFE. However, the system pressure dropped to 0.5 bar, so I refilled it...went too far and now we have 3 bar when cold/standby up to 3.5 bar when heating on.

Loads of advice online on boosting pressure...but how the hell do I reduce it? Don't want landlord involved if poss as we have some issues to sort out with him.