The PO had some fun with your heater cables.
The lever to the right of the steering column operates the Heater Valve AND the flap via a double cable. It would seem a prev Owner perhaps cut the 'missing' cable off??
this website shows the cable required and if you look at the pics provided, how the double cable attaches to the lever bracket.
https://prdesignsf.com/shop?olsPage=products%2Fbowden-cable-for-fresh-air-flap-and-heater-valve&page=2
I have no clue if a double cable for a LHD oriented heater box, would be the same as your RHD oriented one. So, I would contact Jaymic or Linwar in the UK to see if they can get you one. You may get a used one from someone on the UK '02 Board.
http://www.02forum.co.uk/
Pics taken, while I renovated my RHD Heater Box a few years ago, showing the double cable entering the Box. (not the best quality, but you get the idea)