Additional features, settings, or issues not covered by specific Microsoft Teams categories
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Only members for the same organization can be added as Owner for a plan in planner,
You can add or change a member membership from Outlook or Teams in "Manage Teams", see:
https://support.microsoft.com/en-us/office/add-...
If there is more than one owner in a planner team after you has been deactivated your account this plan will still available for the other owner.