Go to https://www.polleverywhere.com/activities . Use the Multiple Choice type to create a new poll, and click Visual Settings > Open Font > Choose the font size you desire.
You will see all your activities/polls. Choose the poll you prepared as your template > Click Select.
Check “Also apply to all presenters existing activities.”
Scroll to the bottom of the page and click Save.
All new polls you create will follow the format of the poll template. For old polls, be sure to perform Sync All within PowerPoint to update the slides/activities WITHOUT re-inserting.