Well that phone should be running Android "Marshmallow", which is the version you would need to make the SD card able to hold apps, so the only other possible issue is if the manufacturer restricted that option on this phone. It happens. Below are the instructions on how to make the card usable in this way. If it doesn't work, then the manufacturer probably did restrict the option.
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...