Additional chat-related features and issues within Microsoft Teams for business
Hi,
If you’re referring to the chat you have with yourself in Microsoft Teams, there currently isn’t a built-in option to delete all messages from that self-chat in one go.
You can delete individual messages by selecting More options (…) > Delete on each message.
If your goal is simply to remove the self-chat and its history from your Chat list and search results, you can use More options (…) > Remove chat history. This only removes the chat from your view; it does not provide a bulk deletion option for the messages themselves.
For more information, please see Microsoft’s documentation: Hide a chat, remove chat history or leave a chat thread in Microsoft Teams | Microsoft Support
If you need to permanently delete a large number of messages at once, this would depend on your organization’s retention/compliance configuration rather than a bulk-delete option available in the Teams client.