How do you move an app from the internal sd card to the external sd card
Moving applications to your external SD card is not possible anymore because Android has changed i's way of managing storage. Your internal storage is now your SD card and your external one is a different, second SD card.

If you'd like to move apps to your external SD card then you have to manually change your external SD's mount point and swap it with the internal one.
Of course this requires you to root your phone.