how do I delete email messages from thunderbird android?

Long press one or more messages to select them, then press the dustbin icon at the top of the screen to delete. You can also setup a left or right swipe action to delete a message. It's configured from settings > general settings > interaction > swipe actions If the dustbin icon is not displayed when viewing an email, navigate to ... Settings > general settings > display > visible message actions Tick the delete action's checkbox.