Here is a step-by-step guide to permanently deleting messages on your iPhone
1. Open the Messages app.
2. In the conversation list, tap Editin the top-left corner, then select Show Recently Deleted, or tap Filters in the top-left corner, then choose Recently Deleted.
3. If you are currently viewing a conversation, tap the Back button to return to the conversation list.
Select the conversations or messages you wish to delete permanently
5. Tap Delete and follow the onscreen instructions to confirm.
By following these steps, users can ensure their messages are completely removed from their Apple devices