For Quectel modules, the IMEI is typically printed on a label on the module shield. You can also read it via the AT command:
Independent users on forums like PINE64 and Quectel Forums have discussed undocumented methods for specific modules like the : quectel change imei
The IMEI is a 15-digit number used to identify valid mobile equipment. The structure generally follows the 3GPP TS 23.003 specification: For Quectel modules, the IMEI is typically printed