Well, to do so your tablet would have to be running Android "Marshmallow". If it isn't, then you won't be able to move most apps there, nor download to the SD card or run apps from the card.
Other, prior, versions of Android don't allow for moving apps to the SD card and running them from it.
If you actually have "Marshmallow" then you can use the instructions below to set it up.
NOTE: Be sure you start with a blank card, as doing this will formate and encode the card, so anything on it already would be gone.
How to turn external SD card into internal storage on "Marshmallow".
1. Go to device “Settings”, then select “Storage”.
2. Select your "SD Card", then tap the “three-dot menu“ (top-right), now select “Settings” from in there.
3. Now select “Format as internal”, and then “Erase & Format”.
4. Your SD Card will now be formatted as internal storage.
5. Reboot your tablet.
NOTE: If you don't reboot the tablet, many things may not work correctly, so make sure you do.