Add a social link to the site footer (Javascript)

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

const footerLinkList = document.getElementsByClassName('footer-links-list')[0]

const liTikTok = document.createElement('li');
const aTikTok = document.createElement('a');
const linkTextTikTok = document.createTextNode("TikTok");

liTikTok.appendChild(aTikTok)
aTikTok.appendChild(linkTextTikTok);
aTikTok.href = "https://www.tiktok.com/@xxxx";
aTikTok.target = "_blank"

footerLinkList.insertBefore(liTikTok, footerLinkList.childNodes[9]);

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.