To do Alt + P M A on Mac in Excel, download and install Accelerator Keys, then press Option, followed by P, M, and A.
Command: Custom Margins
This is how to do Alt + P M A 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 M A opens the Page Setup dialog to the Margins tab where you can set custom top, bottom, left, and right margins. You can also center the content horizontally or vertically on the page and adjust header/footer margins.