Choose File > New from the File menu at the top of your screen, then double-click the template you want to use as the basis for a new template.
Custom templates appear in the My Templates category in the template chooser. If you want to use a custom template that doesn’t appear there, you must first install the custom template (see the instructions above).
Make your changes, choose File > Save Template, then choose an option to save the document as a new template.
The edited template is saved as a new version. You can rename the new version and delete the first version if you don’t want to keep it.
If you’re signed in to the same Apple Account on all your devices and Use the Finder to transfer Pages documents