Excel can be rather confusing. If you try a Print Preview, and then Page Setup, you are unable to set either "Rows to repeat at top" or "Columns to repeat at left". Yet you can set other Page Setup items from this dialog box.
To set your row(s) and/or column(s), you need to select Print Titles from the Page Layout ribbon. This will bring up the same dialog box, but now you can choose the row(s) and/or column(s).