Usage: DEVOICE <#channel> [<nick>]
This will devoice a user or yourself in a channel, but the mode change is done by the server, you need to have AOP or higher access to the channel to use this command on other nicks and VOP access to use it on yourself.
It's particularly useful if you are not opped but need to devoice someone else or yourself quickly.
/devoice #mychannel Zorgor
devoice #mychannel
See also CMODE +o and DEVOICE.
This replaces the service command /CS DEVOICE.