Use the nrfutil 91 imei-write command to write an IMEI number to an IMEI slot of a device of the nRF91 Series.
Warning
The command writes the IMEI number to one-time programmable memory. You can write to each IMEI slot only once.
The command requires that the access port for the application core is open.
If the device is protected, you can open it using nrfutil device recover.