How to Auto-Delete Telegram Messages from Android:
Open Telegram and go to any chat that you want to enable this feature.Click the three-point menu in the top right corner.Choose “Clear History”
“Auto-delete messages in this chat,” select the Auto-delete timer from 24 hours to 7 days.
Then tap “Enable Auto-Delete”
Once enabled, all new messages will be deleted automatically after the specified time
Auto-Delete Messages for iPhone in Telegram
Press and hold the message in the chat that you need to auto-delete.After this tap Choose > Clear Chat in the top left corner after which tap Allow Auto-Delete.That’s it! Your messages in this chat will now be auto-deleted.