-
From the Traces section of the action bar, tap Direct Modification
.
Options are available in the
Graphic Properties
frame at the right of the screen.
-
Move the cursor towards the curve that you want to modify.
The point which is closest to the cursor is activated.

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Drag the selected point to change the shape of the curve.
The vector curve is modified.

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Repeat steps 3 and 4 as desired.
Note:
You can freeze the selection by tapping the curve and unfreeze it either by tapping another curve or by tapping anywhere on the screen.