Make line on one part of the shape disappear (to make one cohesive, but multi-part arm)?

Hi everyone,
I’m following the first module for Harmony Premium Kickstart and I’m trying to make this arm look like one cohesive shape like Jesse does in his “Creating a Peg Hierarchy” video. There’s a gif of my arm and a picture of the one I’m trying to make it look like. My colors aren’t anything like his and I’m focusing on making that line go away right now, where the lower arm and upper arm meet. How do I make that line disappear but keep the shape outlined beyond that elbow?

Thank you for your time!