Solidworks - Round boundary boss across preexisting surface?

I have a model in which I have already used boundary to create a curved surface. I'm wondering if there's a way to fully connect that surface across the flat plane that's at its peak right now.

I'd like to take the surface of Boundary4 in this model and make it rounded all the way across the top.

I'm very new to surface modeling, so bear with me if this is something obvious that I'm not seeing.