if you first click in the source code panel and then Ctrl-F (or Cmd-F if on a Mac), that should bring up a search-and-replace dialog box. You can use the previous/next match buttons to move through the search results.
The Overleaf editor has a Find menu in the top bar which offers a few options, e.g. Find, Find next/previous, Replace, Replace all, etc. After typing in a search expression and hit enter, the first search result will be highlighted. You can then jump to the next search result using the keyboard shortcut
To perform a Replace (All) operation, first type the search expression and hit Enter, and then type the replacement string and hit Enter. Here's a quick demonstration:
Regular expressions work, too: just put
/ around your search expression. You can then refer to capturing groups by
These functions can also be accessed via keyboard shortcuts — you can find a list of all shortcuts available on Overleaf here.