Add a social link to the site footer (Javascript)

Site Settings > Design > Advanced > Javascript (or jQuery)

var li = document.createElement('li');
var a = document.createElement('a');
var linkText = document.createTextNode("TikTok");

li.appendChild(a)
a.appendChild(linkText);
a.href = "https://www.tiktok.com/@xxxxxxxx";
a.target = "_blank"

document.getElementsByClassName('footer-links-list')[0].appendChild(li);

Add the above JS code, replacing the TikTok username on the a.href URL.

Replace linkText with other service name if linking out to something other than TikTok.