It's not uncommon to begin work on a layout before working on the guest list. If you forget to assign which guest list you would like synced to your layout, do not fret! You can easily select which guest list you would like attached to your layout with just a few clicks.
While in your project's layout, simply head over to the Guests tab in the lower portion of the right hand panel and from the drop down menu, select which guest list to sync.
Once chosen, click Select Guest List and you will be good to go!