The eraser tool can be used in the PDF editor either at a document level or bundle level. More guidance on opening documents or bundles in the PDF editor can be found here.
Note: The eraser tool can only be used to erase drawings and freeform highlights made in the PDF editor.
With your document open in the PDF editor, first select the "Pen" tool in the ribbon, and select "Eraser".
With eraser tool selected you can click and drag over your PDF to erase any drawings and freeform highlights.