I am not at my computer, but I believe the Advanced Settings of the Press Button command should have an option for how to click along with an option for a modifier key.
If it is not, then just move the mouse to button (do not click) using that function or a “Move mouse to element” command. Then use the “Send Mouse Click” command. That one for sure has the option for adding a modifier key to the click.
Best of luck!
Disregard
