Microsoft is rolling out an update to make retention policies available for Microsoft Teams.
Completion is scheduled for mid-April.
Please note there is no default retention policy applied to Teams.
To create (and apply) a retention policy for Teams, go to the Security and Compliance center (https://protection.office.com) and reach the Data governance\Retention blade
Then create a new retention policy
Follow the wizard to name your policy and set the retention period and actions as usual
Then, you can choose to retain your Teams channels message and/or your Teams Chats