On Windows you can easily edit a cell formula by hitting the F2 key. This keystroke won’t work if you are using Office for Mac.

In order to edit the formulas in Excel on Mac you’d need to hit Control-U.

There are some alternatives and workaround if you don’t want to change the way you use this feature. On Mac you can install a keyboard remapper like KeyRemap4Macbook and then configure the same keystrokes that you use on Windows.