Email support@mikrotik.com
Detail
RouterOS and Routerboard version
Mobile Operator and the 5g bands the modem can see but is refusing to connect to
enable lte debug logging and send MikroTik the supout.rif file from your Chateau after you have rebooted it and encountered the issue.
LTE debug logging can be enabled from CLI by issuing this command:
/system logging add topics=lte
This article explains how to make a supout.rif file:
https://wiki.mikrotik.com/wiki/Manual:Support_Output_File
MikroTik Support can downgrade your modem, but they require usb storage attaching and an alternate internet connection to work over.
If you cannot offer an alternate internet connection, they will not be able to downgrade your modem.