Cannot Thicken Part..... Any advice?

I imported this part in as a step file. I' am trying to flatten this part but since this sheet metal part is a surface body instead of a solid body. I used a SW add-on Software called LOGOPRESS 3F and used the face merging features. Now I' am trying to thicken this part but it is giving me an error saying Unable to thicken surface/Failed to offset or face could not be deleted. Can anyone help me out?

SolidworksSurfacing