Q: How to mail merge in pages

I don't believe that Pages has a mail merge function at this time.

Check this list.

https://iworkautomation.com/pages/script-tags-data-merge.html

There is no built-in Mail merge capability with any release of Pages v5. There is Mail/Data merge built into Pages '09. And, selected third-party word processing solutions have Mail/Data Merge.

There are a couple of free, third-party custom applications that use AppleScript or custom code to build Mail Merge capability over Pages v5, but only supported by their authors, and not by the rest of us.

1. AppleScript and Pages: Mail Merge
2. Pages 5.5 Mail and Data Merge (posted by its author)

Use Pages '09.

Peter