We will be using realfavicongenerator.net
note: I have no affiliation with that site. Its free, simple and works with no registration required. Also, it outputs favicons of various sizes and formats for a variety of browsers and mobile devices.
First you'll need an image to start with. Their recommendation is: Submit a picture (PNG, JPG, SVG...), at least 70x70. Your picture should be 260x260 or more for optimal results.
after that. Select the XHTML tab for the proper code. Download your favicon package, then extract that zip file to a folder so that you can transfer it to your website. Also, copy the code given. That code goes into Burning Board
Then clear the cache:
ACP > System > Maintenance > Cache
then click the button to Clear Cache.
You may also have to clear your browser cache.
That's it. You should now have browser tab icons or favicons customized to your liking.