The Blue Pencil toolbar has basic tools for deleting Blue Pencil sketches:
on the
Blue Pencil toolbar and drag the cursor across parts of the image you want to erase.

to set a size for the eraser.
on the
Blue Pencil toolbar to wipe all drawings from the active frame.

on the
Blue Pencil toolbar to remove the frame with its drawings from the scene..

The Blue Pencil Marking menu has options for clearing drawings from the scene and deleting layers in the Blue Pencil Layer Manager.