One A/C zone blowing hot 2009 S Class

I have 2009 S320L

Rear nearside A/C zone is blowing hot air even when set to cold.

Car has rear 4 zone A/C with rear controls too.

I understand that its a good chance it is the actuater flap. Is there anything i can do to try and reset it or any ideas before i book it in?

Any help will be much appreciated.