On the Free plan, open the Merge Board from a project to put your branches next to each other and read them in full. Merging them into one answer, and the AI summaries, stay part of the paid plans, and the board tells you so where they would be.
When a conversation grows two or more branches that have answers, a small prompt appears where the branches are, pointing you to the next step. On a paid plan it reads Merge these branches.