How do I restore my IMEI on my LG G3 D851 after flashing custom rom with TWRP?

[Jeff_The_Droid_Enthusiast]

I finally have installed a custom rom for the first time on my new G3. But after having problems with no network, I went back to stock. It seems that everything is back to normal, but my imei is now unknown or null. Is there a way I can fix this?

 

[Rukbat]

Do you still have the box the phone came in (the IMEI would be on that)? Or can you remove the battery (the IMEI is on a label under removable batteries)?

Then there are IMEI changer apps (Google them - I don't know whether the phone is rooted or not, whether there's any data you can't lose, etc.)