To see all the channels in a team, select More channels beneath the list of channels you've favorited in that team.
You can also go to the team name, select More options > Manage team, and then open the Channels tab.

In the Channels tab, auto-favorited channels can be added or removed by team owners.

Tap Teams , then go to the team name, and tap More options
> View channels.
Tap Teams , then go to the team name, and tap More options
> Manage channels.