You need to cut it open along the cylinder.
You can trim 2014 SOLIDWORKS Help - Trim Surface a small gap along the cylinder to do that.
If you are going to use the flatten command in surfaces, you only need to the surface and one vertex.
If you want to to this in sheet metal you can thicken it and use the edge you made by trimming for the edge needed when you use insert bends from the sheet metal commands.
Hope this helps.
Of course it helps. It helps a LOT. My last solution was to cut the surface. Its one step more, but if this is only solution, let it be like that. I need this to export to dwx so it can be printed for sawing pattern. Thank you again
can you attach your file?