Only if you have a full QCN backup. Without that, pay a professional repair shop with a JTAG or Octopus Box (expect to pay $20–$30). Do not download a random ".exe" file from YouTube claiming to "Generate IMEI for LG G8" – those are 100% malware.
Disclaimer: This post is for educational purposes. Altering device identifiers to defraud carriers or hide theft is a crime. Always ensure you are the legal owner of the device and restoring your own data. lg g8 imei repair
LG G8 IMEI Repair: Is It Possible, Safe, or Legal? Only if you have a full QCN backup