Right click on your league of legends icon and click "Open File Location"
Navigate to RADS > Projects > lol_air_client_config_[your server here] > releases > 0.0.0.55 > deploy > lol.properties

Open lol.properties (sometimes named just "lol") using notepad or any text editor, look for where it says xmpp_server_url= and copy the next URL, in my case it is chat.na2.lol.riotgames.com but will be different for you if your not looking under NA.

Open the command prompt again (cmd.exe) as an administrator and type in,
ping [your url] For example for me I'd type ping chat.na2.lol.riotgames.com

Press enter and it will Ping the chat server you typed in giving you the IP address, "Pinging URL [IP here]

Now you will do the same process explained above but switching the IP since you aren't using NA or EUW, replace INSERT_IP_HERE with the IP from your ping.

netsh advfirewall firewall add rule name="lolchat" dir=out remoteip=INSERT_IP_HERE protocol=TCP action=block