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. Press the play button and open up the toolbar (bottom right).
3. Use the slider to move to the trim position. Press play then select forward/backward to move to the trim position more accurately. If the track is long you may have to trim and trim again.
4. At the correct trim position press the scissors to trim the track. Zoom in on the map to ensure you have the correct position.
5. You can trim the track start or end.
6. The track is now trimmed.
7. You can undo the trim by pressing the scissors again.
8. Select Undo to clear the trim.