This post explains in detail how to add a favicon to your White Label.                              

To add a favicon to the White Label page, open the Metadata section in the settings of White Label and post this string in the form:

<link rel = "shortcut icon" type = "image / x-icon" href = "PastHereLinkToFavicon">

Repeat adding code for each page type (Main, Avia result page, Hotels result page, Hotel preview page).

Note! The image should be available on the Internet, and not be only on your local computer.