Here you can Check and download the older version firmware for your LG Phones or tablets By IMEI.
This Page works only if your phone received major OS Upgrade. For Example, Your phone just received the Oreo Update, But you want to download the Android Nougat firmware from LG official.
KK = Android KitKat
LMR1 or LMR2 or L = Android lollipop
MMR1 or MMR2 or M = Android Marshmallow
NMR1 or NMR1 or N = Android Nougat
OMR1 or O = Android Oreo