Team owners and members can change the name of a channel by selecting the channel in the list, then More options > Edit this channel.
If you don't see the Edit this channel option, that means that a team owner has changed the permissions that members have. Also note that you can't change the name of the General channel—that default channel is always called General and is always the first channel in the list.
Team members should go to the desktop or web app to change a channel name.
If you're a team member, tap Teams , go to the team name, and tap More options > Manage channels. Then tap More options next to the channel name and select Update channel.