First define the start position. Move the start selector to the desired position. If you want to set the start position exact to the sound file start, tap two seconds on the start selector and tap in the context menu on „Set to startposition“.
Move the end selector to the desired end position.
To adjust the end of the selection more accurate, double tap before the end of the selection in the orange area to play the last part. Now you can Zoom in and move the end selector more precise.
Tap on Trim to remove the area outside the selection.