If you’re a channel owner, you can share it with people inside or outside your organization from it's channel card. You can also share a channel from the channel options.
Share with people from the channel options
Go to the channel you want to share and select More options
> Share channel > Share with people.Type the names of the people in your org you want to share the channel with and select them from the list. To share with people outside your org, type their email addresses, and select them from the list. Then select Share.
To change a Member to an Owner, select the down arrow to the right of Member, and choose Owner. Then, select Close.
Note
People from outside your org can only be members of a shared channel.
When you share a channel with people, they get a notification and can access the channel right away.
Note
Admins must enable B2B direct connect before you can add people outside your org to a shared channel. To learn more, see Collaborate with external participants in a channel.
Want to learn more? See First things to know about channels.