HELP with uploading new product as FBA and FBM

I am attempting to upload my own product and brand as FBA and FBM in the same listing. I am trying to send some in FBA and then if the style type runs out, it will then start selling my FBM on the same listing. I used to do this but have not done this in years and cannot figure it out with the excel sheet for the life of me….I thought everything was exactly the same but I just used a different sku but I keep getting the error that 2 variations have the same attributes(which they do because I am trying to do 1 FBA and 1 FBM)…IS there also a way when I upload I can assign FBA to the listings…

Thanks in Advance I know this might be a little confusing