Hello I need the same solution for the same problem:
https://community.teltonika-networks.com/11450/idiots-guide-to-band-locking-rut950
I have the same problem but I have device with below parameters:
Product code RUT950GG12C0
Batch number 0021
Hardware revision 0808
Modem Model LE910-EU V2
FW version 20.00.402
Information which I was able to get from router is that I need to lock my band on cell id.
Regards,
Greg