Problem solved. I used David Burke’s very informative blog page on Mail Merge in LibreOffice (Mail Merge in Libreoffice – Technology Against You)
In brief, the Step 4 in MailMerge should be completely disregarded, because it doesn’t seem to work as intended. Instead, use the Edit/Exchange Database access/capability, and just drag the necessary fields you want to use into your document, and make your own salutation.
In Writer, Click Edit then Exchange Database… Then click Browse. Select the file you just made
On the left is a list of data sources. These should include the file you just made. Select it, then Tables, then Sheet1 (or the name of the sheet you want)
You will see the data from the spreadsheet. Click and drag the column you want into your document. For example if I wanted First Name, I would click and drag the First Name column title and not an individual cell like Bob. You will notice it appears gray in your document. You are free to cut and paste it or change the formatting. These words will be replaced with the data in your spreadsheet.