There is a handy page on mw.o to convert discussion pages to flow. However, since it was developed purely as an internal tool, it is pretty unfriendly and error prone right now. At a minimum, it should have some clear text instructions on the page, explaining:
- You need to enter a page title, not a URL
- You probably want to enter a talk page title, not the page title for which you want its talk page to be flow
An example or two would be awesome. And it would be great to better explain how the "initial description" will be used. For that matter, is "initial" description even an accurate description of what that text does?
For that second case (attempting to flow-ify a non-talk page), some kind of warning would be great. But might not be worth implementing, if the instructions are clear enough that it is unlikely to happen. If someone does make that mistake like I did, at least it is reversible.