If you have your transmitter and drone powered on and your device plugged into the transmitter then Botlink can suggest setting up a connection. Tap set up and all you'll need to do is give that connection a nickname since they are unique to each individual model.
Ex. If you have three Phantom 4 Pros, you'll want to name them differently since you won't be able to use a single established connection for the other two.
Once you've connected to your drone the first time you can reconnect by tapping on Drones in the side menu. Start your connection process from one of the profiles by tapping the Connect button or by tapping on the drone's picture and pressing the orange connection button. Once connected you can view details about that specific connection;
The ellipsis on the top-right of the screen will allow you to rename or delete that particular drone profile.