To do Alt + P I on Mac in Excel, download and install Accelerator Keys, then press Option, followed by P and I.
Command: Print Titles
This is how to do Alt + P I on Mac in Excel with Accelerator Keys, the native ribbon and alt key shortcut solution for Mac users who get more done with Excel.
Alt + P I opens the Page Setup dialog to the Sheet tab where you can set rows to repeat at top and columns to repeat at left on every printed page. This ensures headers appear on each page of multi-page printouts.