Best bet is to revert to a back up copy of your file if you have one. Even if it's an old copy, if the header is right, referring to it or copying all layout objects from it may save you effort.
Part Setup... from the Layouts menu can be used to add a new blank header layout part to your layout.
How do I revert back to an old copy?
I was able to add a new blank header, but now I'm unable to figure out how to populate it.
THanks for your help!
First, you'd have to have such back up copies. If you don't have any older copies of your file, this is not possible. If you do, see my response to the newer thread where you reposted. In the future, you can use your OS and/or backup utilities to make copies of your file while the file is closed, you can use Save A Copy As to make copies of your file while it is open or a Filemaker Server back up schedule can make back up copies of your file.
During Development, it's a good idea to make frequent backup copies as a way to protect yourself from "developer remorse" and this can be scripted so that you don't have to keep remembering to do it manually: Saving Sequential Back Ups During Development