Hi Ashley,
Thanks for reaching out.
Usually, it is not possible to add a line break only on a mobile. But you can try duplicating the same Headline element and add the break after the Reveal you want. And then make that visible only for the mobile using the Customize > Hide During BreakPoint and Hide the first one for the specific breakpoints using the same option.

It will be hidden for mobile and visible in desktop and other breakpoints.
It will be visible for mobile and hidden in desktop and other breakpoints.
Hope it helps.
Thanks