If the money has already been distributed from the account you can still roll it into a new plan. This is called an, "indirect rollover." It sounds like you're primarily asking about the logistics: It's actually pretty straightforward so long as you're within the 60-day window and have your cost basis and earnings information (you can call the original plan for this information if you don't have it).
Each 529 plan will have its own process for incoming rollovers. For example, if you were to use the Nextgen program (administered by Merrill Lynch and sponsored by Maine), regardless of whether you open an account or have an existing account there in an incoming rollover form that you would complete along with your deposit. This identifies the incoming funds as a rollover, and the form has a section for completing the aforementioned cost basis and earnings information.
You'll still receive a 1099-Q from the originating plan from the distribution that you made. However, a rollover does not have to be reported to the government; you simply have to make sure the receiving 529 plan knows it is a rollover and receives the tax basis information from the old 529 plan so that it can keep track of the basis going forward.
If you're in this situation you should call the plan and have them walk you through their process to make sure you're completing all the information they require from an administrative perspective.
VP, Research & Development
This information does not constitute tax advice and is provided for informational purposes only. Please consult your tax advisor, financial advisor, local taxing authority, and/or plan provider or sponsor for more information.