We have a whole new roster and so, we have no idea how to transfer the code from android studio to the phone. Please help 
Is this phone already set up from before and you just need to download code, or is it like a brand new phone?
Open Android Studio, make sure your code is open, plug the Robot Controller phone (not driver station) into the computer, find the green arrow at the top of Android Studio, click it, and say yes to the dialogs on the phone and computer.
Edit: This assumes you aren’t using App Inventor.