What are you trying to send? I am guessing it is apps, if this is the case, then it will be dependent on the version of Android you are running. If it isn't at least "Marshmallow" then you won't be able to move apps to the card. If you are running that version, then it is possible that the manufacturer has restricted the option. If you are running "Marshmallow" then you can try the following instructions.
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...