NB: you will need to research bands supported by your carrier before beginning this process

Airtel in Nigeria just introduced a new device offering for those in areas of low network connectivity and for those who wish to make the best of the network in their areas. By partnering with Nokia, they released the Nokia Fastmile Modem alongside the Beacon 1.1 for Outdoor connectivity.
As of 2024, they've been various upgrades of the fastmile to the 5G version as it continues to gain traction among Nigerians as a low-cost starlink. While not mainstream, they still deliver quality 4G reception across most regions in Nigeria.
If you're reading this article, you might be primarily interested in going straight to the point. To save you time, I've summarised the most important points from the original research below.

eARFCN (E-UTRA Absolute Radio Frequency Channel Number)
A unique identifier for the specific frequency channel used in LTE networks.
Purpose: Identifies and tunes to the exact frequency channel within the LTE spectrum.
Example: An eARFCN of 3050 corresponds to a specific frequency in Band 7.
Band Number
Specifies the frequency range or spectrum allocated for LTE use.
Purpose: Identifies the specific frequency range used by operators for LTE services.
Example: Band 7 (2500 MHz to 2690 MHz) is used for high-speed data, while Band 20 (800 MHz) is used for better coverage and penetration.
PCI (Physical Cell Identity)
A unique identifier for a cell in an LTE network.
Purpose: Differentiates between cells, ensuring the user equipment can distinguish signals from different cells.
Range: PCI values range from 0 to 503.
Example: A PCI of 273 identifies a specific cell within the network.

Cells
cells are the fundamental units that provide wireless coverage to specific geographic areas, each served by a base station or cell tower. The primary purpose of cells is to ensure seamless connectivity and manage network capacity efficiently by dividing large areas into smaller sections. Cells vary in size from large macrocells, which cover expansive rural or suburban regions, to smaller microcells, picocells, and femtocells, which cater to high-density urban areas and specific indoor locations.

Carrier Lock
Most of the devices I've encountered have a carrier lock on them. However, it can be worked around to use other carriers by booting it with the carrier-locked sim, then when connected, eject the sim and wait for it to disconnect before inserting another sim. The downside of this is that once it goes off, it locks the device and will need the carrier it's locked to, to be inserted for a fresh boot.".
you can also do some of your research to see if this can be bypassed.

Getting 'Admin' WebUI Access and Changing Network Bands
The WebUI includes an installer admin privilege level that provides access to advanced functionality beyond what is available on the companion app. The credentials to access this are as follows: Username: fm2-installer, Password: Y$Gb7GVg. Please note that these details may vary from device to device, and further research may be required to ensure accuracy.

Once logged in, on the status page, perform a cell check measurement, this will disconnect you briefly for its duration. Once done you'll be presented with the various bands available for your carrier.

next you take those details, and put them in a frequency finder such as cellmapper https://www.cellmapper.net/arfcn?net=LTE&ARFCN=9360&MCC=0

using cellmapper, you get the band details, eARFCN, and Band Number, cross-checking this with the bands supported in your fastmile under the network section. if supported enable it/them in the band list

to switch from a specific band to another, click on the add cell option under the network section and fill the relevant details as gotten from the measurement and cellmapper