There are 2 ways to shout.
A) If you purchased the Master rank on creative then you have the ability to shout at any time.
![Glasses 8-) 8-)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
If you're not a Master rank, then you can go to
www.snapcraft.net/vote and vote for shout for 2 hours. Make sure to actually be on the creative server when you vote or else it won't work.
Command: ! <Msg>