Trans Error Message

We just replaced the instrument cluster in my '91 525i( my son got a ticket because the speedo was not working in cold weather ). Bought a used unit from Ebay and had it installed by a local mechanic. When my son picked the car up and started it the Trans Program light came up and the car dings about every 5 seconds. The car was running fine prior. The mechanic told my son the problem relates to us buying the part on Ebay.

Too coincidental for it to not be related to the new part. How should we troubleshoot/ make the message and bell go away?

TIA,
Berry

i bought a cluster from ebay also few months ago, i installed it without remove the chip on the back of the cluster and it gave different reading like: mileage and oil service inspection lights (was giving me info from the bimmer cluster came from). i remove the chip from my old cluster and but it in the ebay cluster and everything came back normal. showed back my correct info.
don't know if it will work, just sharing similar experience.

did the mechanic swap the chips from the cluster?

All of the info that was showing on the old cluster is showing now, too. I'm stumped.