I had to 'recalibrate' mine when I installed custom made 300km/h dials where I had to remove the needles...
Was a bit of a long process of trial and error, but basically I had to reinstall the needles, then drive and compare the speed on the pfc hand controller to what the needle was showing, then stop and adjust accordingly, re-test and repeat until they matched.
Bit of a tedious process, and had to be very careful with the needles, but had it perfect in the end...
Not sure what's caused your problem though, so the solution may be different.