I am afraid that once you changed it, it was simply gone.
The only possible way you could recover it was if and only if you had created a gedcom of the file between the time you finished the initial data entry on that record and the time you made the name change of that field from "Event" to "Marriage Bond".
But then you'd need to be pretty skilled at finding your way around inside a (dot)ged file, no matter how small or large the gedcom was. Not many people can do it because it's not a skill much called for, even while it can 'save your bacon' on occasion.
A (dot)ged file is typically a straight text file, so if you simply rename it to a (dot)txt extension, you can view it with Windows Notepad and use the global find option to search for that particular individual. Maybe then you could have gotten it back. But I don't advise altering any of the records within a gedcom. That, too, takes skill to prevent total disasters in a future use of that gedcom, such as cross-linked spouses, or individuals who are their own maternal or paternal grand or great-grandparent, or something even worse.