You can trim the start or end of a track with the trim tool.
1. Select the track in history and select map view.
2. Open up the toolbar (bottom right).
3. Press the play button.
4. Use the slider to move to the trim position. Press play then select forward/backward to move the cursor to the trim position more accurately. If the track is long you may have to trim and trim again.
5. At the correct trim position press the scissors to trim the track. You can zoom in on the map to ensure you have the correct position.
5. If the cursor is more than half-way along the track this will trim the track end. To trim the beginning of the track the cursor must be be less than halfway along the track.
6. The track is now trimmed.
6. You can undo the trim by pressing the scissors again.