Can someone help with a Swift / Xcode error code [on hold]

I am trying to submit an app to the app store (first time), had both iTunes connect and Xcode open at the same time trying to get profiles and certificates back and forth, and downloaded. At one point I notice

Apple Mach-O Linker Error Linker command failed with exit code 1

in the left pane. What did I do, and how can I fix it. I had the app working on both my iPhone and iPad but now it will not even build. Please help I am looking at lots of work out the window.