The text pane supports Find & Replace for $Text. Opened via the Edit -> Find menu or a shortcut, this adds a two-row toolbar to the top pf the text pane (and beneath any Key Attributes).
Existing Find controls can be used to cycle through the current note's Find matches and replace them (Replace button) with the Replace text. Or, use the All button to replace just the current match.
In the Text pane, Edit ▸ Find ▸ Use Selection for Find (from v6.6.2) loads the find string for both the text pane search bar and the view pane search bar.