Well, unless the tablet is running Android "Marshmallow" you cannot get the apps to download or move to the SD card.
Now if you are running "Marshmallow" then you should be able to (unless the manufacturer has restricted that option, which some do.)
If you are running "Marshmallow", or can upgrade to it, then to start, make sure the SD card you are wanting to use is blank. Why? Well, because when the card is formatted and encoded to work with only your device, it will be wiped of any data that was on it.
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 phone.
NOTE: If you don't reboot the phone, many things may not work correctly, so make sure you do.