There are two methods to disable Teams Echo bot. Due to no Teams echo in my lab, I use 15Five app to demonstrate the steps as below.
One is to block this app in Microsoft Teams admin center > Teams apps: Manage apps > select Teams Echo app > Click Block button.
Another is to block this app in Microsoft Teams admin center > Teams apps: Permission policies > enter into Global (Org-wide default) policy > in Third-party apps section, select Block specific apps and allow all others > Then, add apps you want to block.
For more information, please refer to this article.
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