Well, an SD card when installed normally is made "External" storage, which most apps can't run on. They require "Internal" storage.
Now, if your tablet has, or can be upgraded to, Android "Marshmallow" or newer, then you 'may' be able to make the SD card "Internal" storage. Try the instructions below. Again, you must have one of the versions of Android the instructions are for. Doesn't work on other/prior versions. Also, the device must allow the changes. If any of the changes don't work on your device (and the version is good) or any of the steps you need to take on the device are missing, then the manufacturer has restricted this change on your device.
How to turn the "External" SD card into "Internal" storage on "Marshmallow"...