In the past, you could convert section headings back into regular tasks by deleting the colon in the task name. However, in the current version of Asana I don’t see a way to do this.
The problem I’m trying to fix, is that we have some users who assign people and deadlines to section headings, which is a weird and wacky method. It creates task lists that are hard to read, doesn’t work well with the My Tasks view, etc. I would love to be able to convert those sections into regular tasks, but I don’t see a way to do it, other than a somewhat laborious copy and paste process of moving all the details into new tasks.