A family of Microsoft word processing software products for creating web, email, and print documents.
An ordinary Find/Replace done from the document body will update the body, headers and footers.
If you want to process footers only, and the Sections use footers that are not linked and/or you're using a 'different first page' page setup and/or a 'different odd and even' page setup, you will have to process each of these separately. That process could be automated with a macro.