First, get the motors, controllers, power supplies, and Arduino wired and running.
Then, write code to send the control parameters to the Arduino from the Serial monitor. Robin2's tutorial on Serial communications is a good reference, Serial Input Basics - updated - Introductory Tutorials - Arduino Forum
Then, you can move to Bluetooth, and if you use the module on the hardware serial pins you will not have to change the Arduino code. The BT will just replace the serial monitor.
I do not have an app and don't know anything about that haha.
To send and receive the messages to the BT you can probably use a standard Terminal App. I use this one.
There are several function buttons for sending pre-formatted messages.
If the standard terminal does not meet your needs, you can look for a motor control app which I'm sure exists. Alternatively you can write our own app with MIT App Inventor 2.