pmcvay

I am using onshape to build a part. There is an area where I need custom support structures. I built the support structure in onshape as a separate part (so I have the main part file and the support part within the same part studio). How do I export the two parts in a way where I can later specify in Cura that one should be a support and one should be the main part? When I select both and export as STL, cura views the two parts as one part and I cannot turn the one into support material