Obviously you have to remove the entire under cowling/fender.
Tip for removal: cut a section of the loop around the hose to help get the undertail out easy.
First scribe a line with the tip of the x-acto following the inner lip, then cut it through.
I used masking tape to mark the line to cut for the sides.
I rolled the edges with a sanding drum on my dremel and finished it by hand.
I used a heat gun to clean up the edges.
The left and right views of the finished fender.
NEW REVISION (done during HMF install)
I removed the undertail again and scored along the mold edge with an X-acto blade.
I used an coarse rasp to work the contours, then sanded it smooth.
Final step was to use the heat gun to blend it all nice.