Well it depends on what version of Android the phone is running. Anything lower than "Marshmallow" will not allow for making the SD card "Internal" storage, which is what it would need to do for using apps. It would also depend on, even if you have "Marshmallow" if the manufacturer has restricted that option on the device. It happens. If you have "Marshmallow" or can upgrade to it,follow the instructions 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 phone.
NOTE: If you don't reboot the phone, many things may not work correctly, so make sure you do.