Hi Alex,

Thank you for contacting us.

Existing icon that you are not currently using has to be replaced 

for example if you are using an icon like behance icon.

You need to first install the following plugin https://wordpress.org/plugins/font-awesome/ . 

Use the following custom css to replace behance icon with tiktok icon in the header

.fa-behance:before {    content: "\e07b";
}
#header-outer #social-in-menu a i.fa-behance:after {    content: "\e07b";
}

Enabled in Salient > Header navigation > Layout related.

Hope this helps.

Kind Regards.