I apologize our previous responses did not help to answer your question. So thank you for sharing your feedback on wanting to change this text! One way you can do this is by changing the font under the design tab of your campaign.
Making this update will change the font in the action block, just not the buttons. Being able to customize all formatting in these RSVP blocks, such as font and text size, is a feature request I have submitted to our Product Team in the meanwhile.
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