The second step of the one-handed backhand is to change your grip to one that is appropriate when hitting this shot. There is a range of grips you can use and these are covered in the grips section of the website (hyperlink!).
The way you change your grip is to relax your hitting hand, the one holding the handle. This is your right hand if you are right handed. It’s the opposite for left handers. Use your non-hitting hand, which should be holding the tennis racket at the throat, to rotate the racket around until you reach an appropriate one-handed backhand grip with your hitting hand. Then re-grip the racket.
In the video, you’ll notice that I change my grip and angle the racket head up at the same time. As a result, this step happens in tandem with the pivot and shoulder turn (the previous step).