Hello @Yunus KALDIRIM
Thank you for your feedback.
At the moment, Microsoft Teams does not provide a built-in option to clear all of your personal chat history at once. While you can delete individual chat messages from your view or hide chat conversations, there is currently no "one-click" feature that allows users to remove their entire chat history in Teams.
If you are using Teams in a business environment, your IT administrator can configure Microsoft Teams retention policies through Microsoft Purview to automatically delete chat messages after a specific period of time, depending on your organization's requirements.

Since you mentioned that you would like to see this functionality added, I encourage you to submit feedback through the Microsoft Feedback Portal or directly from within the Teams app. Microsoft relies heavily on user feedback when evaluating and prioritizing new features and improvements.
Reference: https://support.microsoft.com/en-us/office/how-do-i-give-feedback-on-microsoft-365
I hope this information is helpful. Thank you for your understanding.
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