@Mani
It's possible that the external user's account has not been fully provisioned yet. When a guest is added to a team, it can take up to 24 hours for their account to be fully provisioned and for them to have access to all the features of Teams.
If it has been more than 24 hours since the guest accepted the invitation and they still cannot change the organization in Teams, there may be an issue with their account permissions. In this case, you may need to check the settings for the guest user in the Azure Active Directory portal to ensure that they have the appropriate permissions to access Teams.
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