I'm guessing the title was entered in the database with a period at the end. Remove it and let the format deal with adding periods if you want to do that.
You can't use RegEx for find/replace. But you can use Global Change -> Search and Replace, searching only the Title field for . (period) and replacing it with nothing. There may be the odd title you have that has a period in the middle somewhere, but they'd be rare. And in those few cases (if any) you could add them back.
If you want to do this on just the references you're citing, you can scan the document first and then do the find/replace on the Hits (which will consist of the references you're citing).