The social icons come from Font Awesome. There is a FA glyph for TikTok, but it may not be part of your FA kit. Assuming you get it incorporated, changing the span element’s classes (within the TikTok anchor link) to "fa-brands fa-tiktok" will cause the correct logo to be used.
How to alter span classes? IDK, sorry. It depends on how the social menu items are implemented. You should ask through the dedicated support channel of whatever module is responsible for the social menu.
Another approach would be to override the existing CSS with custom styling. Upload an image file of the logo and set it as the background for the span element. You’ll also need to define the element’s size and set it to display as a block.
@bcworkz
I will contact the theme developers and see if they have a solution. I changed the “fa” in the code and the icon disappeared.
Thanks.