How can I work around this...?

I recently received a Nintendo Switch in a trade. The screen was broken, so it was removed. But, the system worked fine in the dock. It also didn’t come with joycons. However, a pro controller was included. I was able to verify that the system works in the dock, on the TV. My issue is this: I thought I could reset the system to link it to my Nintendo account. When I reset the system, it now shows the graphic for attaching the joycons while it’s in the dock. I borrowed a pair of joycons from my cousin. However, my system is not recognizing anything is attached. The joycons or the controller. The joycons have power. How can I get my system set up so I can actually play games on it?