Two ways to modify the tomcat icon
The first: under ROOT under tomacat's webapps:
Find the favicon.ico icon and cover it with your own small icon.
Just restart the server.
The second: Introduce in the page, as follows:
<link rel="shortcut icon" href="../images/favicon.ico" type="image/x-icon" />
The path of the icon is filled in the href.
Just refresh the page directly.