Well it is going to depend on what version of Android the tablet is running. If it is running anything less than "Marshmallow" then you won't be able to make the SD card the "Internal" storage rather than "External" storage, which is what would be needed. If you aren't already running that, you can see if you can upgrade it to "Marshmallow".
Also, the manufacturer could have restricted this option, even if you are running "Marshmallow". The instructions on how to turn the SD card "Internal" are below.
How to turn external SD card into internal storage on "Marshmallow".
NOTE: Please be sure you start with a blank SD card. It needs to be blank because when the card is converted to "Internal" storage, it will be formatted (wiped) and encoded (making the cards data only readable by that device).
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.