It's not as simple as that. Some boards have manual adjustors, only later ones have this feature. Also, it's not a cure all, some boards wont reset if they are faulty. Half the time you will need a new PCB if this has just happened spontaneously.
First, have you checked the hose and wand? By taking both off and looking down them?
The board reset is a more complicated procedure than you have been told, you need a torch with a certain number of lumens, preferably with the machine top off and using a restrictor tool on the hose, and there is a sequence. It took our tech about a dozen tries with instruction from the Sebo rep before he got it. It's not just shining a torch somewhere and not something you can easily teach on the internet. And you need the tool anyway.
If you're certain the hose and wand are clear, it's probably one for your local Sebo dealer. Or we can do it if you send the head using our service >here<