The link seems to be broken (well, not exactly broken but it shows a search of “primavera p6” images, and I am not sure what I am supposed to see on those images). Anyway, create two top-level tasks for your projects and move tasks into appropriate top-level task.
I am trying to create a SPLIT or BREAK TASK. like we are having the dotted line. How can this be done? I am new to this gantchart software. Never used any.