A QCN (Qualcomm Calibration Network) file contains all radio calibration data, including IMEI. Using feature, you can restore a known good QCN from a donor device (after nullifying its IMEI to avoid duplication).

Restoring these from a clean backup instantly fixes IMEI issues.

: Some Android apps like IMEI Changer exist but generally require a rooted device and the Xposed Framework to function. Legal and Safety Implications [GUIDE] How to change IMEI on Snapdragon devices

: A specialized utility for writing identification numbers to Snapdragon chipsets.

An "IMEI repair APK" is an Android application package file that claims to rewrite, restore, or change the IMEI number of a Qualcomm-based smartphone directly from the Android operating system, without requiring a PC or specialized box (like the Octopus or Z3X boxes).