First you need to vote https://l2reborn.com/reward/ and then, 5 minutes later you can use !! prefix to global shout.
Example: !!EE 5x LFP!
Only 2 global shouts allowed each 12 hours.
Minimium level required: 20
Note: Even if you have donated to the permanent VIP you also have to vote every time you want to use the global shout.