Google Sheets has a powerful find and replace function. But you may want to use Google Apps Script to do the same job. StackOverflow has a question on this. The accepted answer would require you to loop through all cells, find the text, replace it and post the new text back to the cell. Google Apps Script has a more powerful, and simpler, method called TextFinder.
Usual post highlighting the TextFinder method which you can use to find and replace text in Google Sheets. The post has more information about this method and how to use it.
