Even out a run by alternating tempos
When a fast run in one hand comes out uneven, Alternating tempos leaves the score as it is and plays the run to you once, slowly. You play it slow, then at the speed you were playing, and the same again; the app sets the speed for each take. A last take at your speed shows whether the run now comes out more even. Only the run's hand is listened to; the other hand can play along or rest.
After a take, choose Practice alternating tempos
It's right under the button that polishes those bars in the result; if that button shows another drill, pick it from Other practice next to it. While you're practising a spot, Other practice in the bar at the bottom opens it too.
Listen once, then play four takes, slow and fast in turn
The score stays as written; what changes is the speed, and the app sets it for you. The first take is a good deal slower than you were playing, the second is at your speed, and the third and fourth go the same way. After each take you see whether the next one is slow or fast. If a note went missing, the result says so and you play that take once more at the same speed.
Play the run once more at your speed
The last take is at the speed you came in at, and you see whether the run came out more even than at first. This take carries on your practice of the spot at that speed. Start alternating tempos again whenever you like, or simply keep repeating.
What is secure slowly doesn't carry over to the fast speed by itself: the hand has to practise the movement at the speed it will be played. Going back and forth carries it across. In the slow take you hear and place every note, and in the take at speed you check that it holds. Two fixed speeds in turn work better than many different ones, and it always ends at the speed you started from, because that is where the run has to work.