Here is Motorola’s guide on using the SD card in the Moto G4:
Once a card has been formatted as internal storage, both your device internal storage and the card will show up as “device storage” under storage settings, and you will be able to move applications which were in internal storage to the card. Moving applications to the card can be done from application settings (Settings > Apps > select application > Change storage location).
I’ll admit that I’ve never attempted to move an app manually once I’ve formatted a card for internal storage. I generally migrate data on the device to the card when presented with the option after formatting.