Set Excel as default instead of Numbers

See the following from Choose an app to open a file on Mac - Apple Support

Permanently change the app used to open a file

1. On your Mac, click the Finder icon in the Dock to open a Finder window.
2. Select the file, then choose File > Get Info.
3. You can also Control-click the file, then choose Get Info.
4. In the Info window, click the disclosure triangle next to “Open with.”
5. Click the pop-up menu, then choose the app.
6. To open all files of this type with this app, click Change All.