Slack.com Leaving a channel
Just as you can freely browse and join channels, you can also choose to leave them, or come and go as needed.
To leave a channel, just click the channel name to open the Channel Menu, then selectLeave channel. Or, just type /leave.
If you leave a private channel, you will lose access to the channel and its archives. The group’s messages and files will no longer appear in your search results. To rejoin a private channel, someone in that channel must re-invite you.
Leaving a channel with a Restricted Account
When a team member with a Restricted Account leaves a channel, they must be invited back to it — they cannot rejoin it on their own.