Hello, Miguel ,
IMEI changes on the device side.
From the platform and application side, this cannot be done.
In this case, you need to check with the manufacturer or dealer how to roll back the tracker to the original ID and ask why the device ID can change on its own.
You can also try to change the IMEI yourself using commands to the device. The necessary commands can be found in the instructions for the device, perhaps this will help.