How to retrieve deleted text messages on iPhone 7 Plus?

Depending on how long ago you deleted the text, see this.

If Messages in iCloud is enabled, the messages cannot be retrieved. If you're unsure if this feature is turned on, here's how to check: Use Messages in iCloud. If Messages in iCloud isn't turned on, and you have a backup that contains the messages, they can be restored with these steps: Restore your iPhone, iPad, or iPod touch from a backup. Keep in mind, any data that has been put onto your iPhone after the backup was created will be lost. If you have made a backup of the iPhone since you deleted the message, you will not be able to retrieve it either.

Delete a message or conversation

When you delete a message or conversation, you can't get it back. So make sure that you save important information from your messages.