Adding a social media icon

Hello!
I want to add the Untappd social media icon to my footer alongside the Facebook and Instagram icons, but this Untappd icon is not available.

How can I do this on the Twenty-Twenty theme?

A google search found someone else had asked this on another theme and it was added to the icons. But I don’t see it available for this theme.

For reference to the other forum post from over 2 years ago:

https://wordpress.org/support/topic/add-untappd-to-social-media-icons/

Thank you!

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