The Find & Replace feature was not removed, but the way it is named in the menu (simply Find...) and the UI which requires the user to click on a small arrow to access it may be confusing. Please see the GIF below which demonstrates how to use the search & replace feature:
If you need a slightly more powerful refactoring tool (i.e. distinguishing the variable scopes) you may want to check out my jupyterlab-lsp project which now includes support for the rename action (see here for a demonstration GIF, but please install a newer version, not the tag linked).