Hi Raewyn,
Here is a forum discussion which involves mail merge using a tool called ‘Autocrat’. This is a more sophisticated use case – skip the posts that don’t relate to Autocrat!
There are actually about 4 tools that will do mail merge, autocrat is my favourite. So if inside a Google Sheet, if you go to Add ons > Get add ons… and search for mail merge you’ll see a few options.
Rob