The Eraser tool is found at the top of the Tool Dock.
When selected, it slides out in a similar fashion to the drawing tools and has two modes it can be used in.
In normal mode, the eraser can be drawn with like a traditional eraser. You can choose the size, and a hard or soft edge.
Flow’s stroke eraser removes entire strokes as you touch them. You can toggle which types of tool the eraser will be able to delete.
To clear the entire document, press and hold on the eraser until the dialogue box appears.