Fuel level indicator GS 1200?

I have recently had a GSA tank fitted to my std GS, so now carry 33l of petrol. Anybody know - as it was suggested to me on the week-end - how I go about calibrating the whole thing - do I need to take it in to BMW - please no!! - or can it be done another way. The problem is now the display constantly gives me the warning tri-angle saying I have 0km left, and I will have no indication other than my calculations as to how much I have left :-\

Any input appreciated :thumleft: