Does your vehicle have AFS ?
No there is no headlight levelling switch inside, but as, Picasso states, it should all be 'automatic' if the rear sensor is UK.
Have you changed your wheels and/or tyres lately?
Every year, for some strange reason, my headlights may need minor realigning.
I wonder whether that has anything to do with the load in the vehicle at that time
Picasso's point is important too.
Notwithstanding that, it is a simple task provided you have the correct gear, i.e what they have at the MOT station.
There is a manual method involving a flat, in front of a wall at a fixed distance, etc. etc; not the way to go in my opinion