This may help
Manage Alexa settings and delete data via the Alexa app (More > Settings > Alexa Privacy) or online at Amazon Alexa Privacy Settings. You can delete voice recordings by voice, individually, by date range, or set them to auto-delete after 3/18 months. Devices can be removed in the app under Devices > [Device] > Settings > Trash.
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Alexa Privacy & Data Deletion
Voice Deletion: Enable "Delete voice recordings by voice" in the app under "Manage Your Alexa Data" to use commands like "Alexa, delete what I just said".
Delete All History: Go to More > Alexa Privacy > Review Voice History, change the filter to "All History," and select "Delete all my recordings".
Automatic Deletion: In Alexa Privacy, choose to keep recordings for 3 months, 18 months, or not at all.