Tested on non-rooted LG G5 H850 with stock Android Oreo 8.0. What info have I gathered:
To move app from internal storage to external SD card storage go through this steps: Settings -> Apps and notifications -> App info -> select app -> Storage -> Storage used change -> select SD card.
But not all the apps have a feature to move itself to SD card. You can easily check availability of such feature using "Apk Analyzer app by Martin Styk" - just look at "Install location" field (tap on field for explanation).
Here you are two pairs of screenshots, where shown:
1. how does look app info, if the app have "move to sd card" feature
2. and how does it look, if the app doesn't have such a feature