Well, depending on your phone, it may not allow for saving apps to the SD card. Most phones do not have this option. Since your phone should be running Android "Lollipop" you would not be able to save to the card as it requires you have Android "Marshmallow". Now if you can upgrade the phone to "Marshmallow", or already have, then it is going to depend on if your phones manufacturer has restricted the option or not.
Below are the instructions on how to make the SD card "Internal" storage, which is what would be needed to save apps to the card.
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.