Well that particular phone comes with Android "Lollipop" and you would need "Marshmallow" to set the SD card as the default storage for apps. If you can upgrade the phone to "Marshmallow" then the instructions below will help you get the card setup. However, if you can't upgrade the phone to that version of Android, then you cannot set up the card to accept apps.
NOTE: If you can get it to "Marshmallow" you will have to start this process with a 'blank' SD card. Why? Well because the card will be formatted and encoded when the change is made from "External" to "Internal" storage. This will wipe any data that was on the card and will make the cards data unreadable by any other devices.
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.