Changing local time on Digital/Analogue tachographs

Actrosman:
how do i change the time on the one my Actros? It’s normally in for a ‘service’ this time of year so mickanicks do it. Its a ‘digital’ type display but is analogue…ta

If it’s the type bellow or similar:

It’s a long time since I’ve done this but as far as I can remember before inserting a chart you press the M button then press the + or - buttons to adjust the time then press the M button again.

It’s not too clear but you can just see the M (memory) and +/- buttons on the right side of the tachograph.