Eraser

Erase parts of the drawing

Eraser

Select the Eraser tool, and click anywhere you want to erase.

The eraser size is directly related to the grid size. Try temporarily changing the grid Units if you want to make the eraser bigger.

Undo

The Undo button may be a better option in many cases. It will undo the last thing that was drawn. You can use it repeatedly to undo more than one thing.