Septuplets are a figure that is a little difficult to grasp at first since it is an unusual one in our musical culture. Be careful and listen closely to the different strokes; since this an odd figure, if you start the first beat with your right hand, you will start the second with your left, and so on. This is a very good exercise to master the different figures and their combinations.

Work at low speeds so that you can clearly hear all the values and control the rhythmic changes. Be careful when changing from one figure to another to avoid mordents. Be very exacting with yourself in your first steps.
Then lower the speed by 5-point intervals until you reach 40. Once you have done this you can increase the speed until you reach your limit.