There are several reasons a user might seek to repair or change their device's IMEI:

: If you rooted your LG G8 and made a backup of the EFS/Modem partitions using TWRP or a similar tool, you can simply restore that backup to fix the issue. Critical Legal and Safety Warnings

Repairing an LG G8 IMEI is significantly more difficult than older LG models (like the G4 or G5). The G8 uses Qualcomm's secure boot architecture, meaning you cannot simply write a file via Fastboot or ADB.