My forum is and I want to add favicon/bookmark who can guide me
Using a very special function called "search", I found this for you:
https://www.simplemachines.org/community/index.php?topic=236748
there is also https://wiki.simplemachines.org/smf/Favicon.ico
As a rule, all modern browsers know how to ask for one. So just upload your own in the forum's webroot.