You'll need to head to your dealer, the vehicle will need reprogramming in order to recognize the new cluster, the mileage is stored in the IPC(Instrument Panel Cluster).
Until you do that, the new cluster will remain frozen at the mileage of the vehicle it was removed from, when reprogrammed the vehicle and cluster will able to communicate and it will reflect your actual mileage.
We won it, we won it, we won it!!! RDE 2/15/98
"Steam engines don't answer back. You can belt them with a hammer and they say nowt." - Fred Dibnah MBE (April 28, 1938- November 6, 2004)