How can I fix the "Non-descriptive link content"?

I want to fix the “Non-descriptive link content” warning from my site, whose read-only link is published below. The warning appears at the three social links (the ones with LinkedIn, Stack Overflow and GitHub logos). I tried to read the help, but I don’t understand where, exactly, should I go to fix this error.

Can you help me?

Live link: here

Here is my site Read-Only: LINK
(how to share your site Read-Only link)