USB Debugging and OEM unlock needs to be turned on within the developer options to unlock the bootloader of LG K20 Plus. However, if you’ll look for developer options in Settings, you won’t find it anywhere.
In the earlier versions of Android, developer mode had quite a few options so it was kept visible by default. Since Lollipop, many more features are added which are meant for developers only and a normal user can do more harm than good by messing up with these settings. So keeping in mind the majority of the users its kept hidden but can be enabled quite easily with few taps on Build Number. Let’s see how to do this.
How to enable USB Debugging on LG K20 Plus