Viewing Messages:
Open the 2nd Phone Number app.
Tap the "Messages" tab at the bottom of the screen. This will show your entire message history.
Tap on a specific contact or phone number to see your conversation with them.
Deleting Messages:
Follow steps 1 and 2 above to access your message history.
Swipe your finger left on the contact or number whose message you want to delete.
You see a "Three dots" option appear. Tap on it to reveal additional options.
Select "Delete" from the list of options.
Confirm the deletion by tapping "OK".
Remember: Deleted messages are permanent! Make sure you really want to delete them before confirming.