The IMEI is a 15-digit number used to identify valid mobile equipment. The structure generally follows the 3GPP TS 23.003 specification:

Restart the module and send AT+GSN to confirm the change has been applied. Limitations and Firmware Variations

Quectel provides an official method for authorized customers:

Since many Quectel modules are based on Qualcomm chipsets, QPST can be used to browse NVdata and modify IMEI files, though this typically requires specific manufacturer permissions.