There are already threads here discussing exactly that. Did you do a search?
For a bulk Find/Replace that uses an Excel workbook as the data source to process all documents in a folder, see:
https://www.msofficeforums.com/word/...html#post34254. For an interactive version that processes just the active document, see:
https://www.msofficeforums.com/word-...html#post31849. Later in the same thread there is a discussion on how to convert the interactive code to automatic replacement.