Find and Replace Text for Sketch allows you to search throughout your active document and replace text within canvas elements (symbol overrides included). You can also choose to perform a rename on just the layer names as well. Searches can be scoped at the following levels based on your current layer list selection: Document, Page, Artboard, Layer
Download the latest release, unzip then double-click
find-and-replace-text.sketchplugin to install.
Launch Find and Replace Text from the Plugins menu or use the keyboard shortcut, CMD+SHIFT+F.