Yeah man just when you feel confident/ready book a manual driving test in person through your nearest RMS.
In terms of driving, you are going to have to ask your full licensed friend to help you master the basics of the manual car since I assume you are going to go to the driving test with that.
Do hill starts, hold the car with the clutch (but only for a few seconds) or else you will wear out the clutch, basically get to know the clutch of that car, do 3-point turns, etc etc. I'm sure you'll pick it quite quickly man, especially since you already have your P's and drive. Once you start learning manual competently, then it will just become second nature.