You can ask admins to assign your server to your clan or set the clanflag HERE.
Besides asking admins to set your server to your clan, you can also let this be done automaticly by adding something in your server configuatation file!
sets tb_clanid "<clan_id>"
You need to replace <clan_id> by your own clanid, which you can find on your clanpage too.
So, if you (for example) set this in your server config:
sets tb_clanid "69291"
If you add this to your server.cfg and restart the server, the system will automaticly assign your server to the clan with the id of 69291