Trim

You can use the Trim tool to get rid of unwanted lines and edges. The tool deletes the lines between two points/crossings. Here's how to do it:

1. Create a sketch, open the Sketch menu by tapping on any sketch, then tap on Trim 

2. Tap on the unwanted sketches.

3. When you are finished, tap on Pen, Back or anywhere on the grid to exit the tool.