Guest users are unable to access Teams channel

Hello Hieuchaya 

welcome to the Microsoft community, my name is Recep I'll be happy to help you today.

I understand that your guest users are unable to access a teams channels with "error message you’ll need permissions to access this team or channel. try contacting the team owner or admin.".

1. Check the guest permissions for channels. To do this, go to the team name, select More options > Manage team, then select Settings > Guest permissions. Make sure that the permissions you want to allow are checked.
2.Are you also an admin user besides being a channel owner? If not, please have your organization's admin user check and make sure your organization's settings is set to allow external user/guest users.

3.Also, on the guest users' side, make sure they are using the Teams for Work or School edition, not the Teams for Home app

4.Clear cache and refresh: Instruct affected members to clear their browser cache and refresh their Teams application. Sometimes, caching issues can cause inconsistencies in accessing channels or seeing updated information.