Where is a "Save As" button in Excel on my MAC Pro to save as a New File Name?
File menu > Save As... or  Cmd ⌘   Shift ⇧   S  



If you specifically want a button in the button bar, then View > Toolbars > Customise Toolbars &amp; Menus > Commands, then Find it in the File section &amp; drag to where you want it in the toolbar. [Note, Save as doesn't have an icon, so it will appear there in words.]