How do I download "Messenger Kids" on an iPhone 7?

Meta Messenger Kids requires an iPhone 7 or newer, running iOS 13.4 or later.

To see which version this iPhone is running (and which iPhone model), see Settings > General > About

Here is how to: Update your iPhone or iPad - Apple Support

And what to do: If your iPhone or iPad won't update - Apple Support

If this iPhone is new to you and has not been reset by its owner, the owner will need to release and reset it now:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Messenger Kids is billed as a "messaging app for kids."

iPhones support the ability to set up parental controls which include the ability to block children from downloading apps without permission.

Is your iPhone 7 subject to parental controls? If so, you may need to approach your parents and get permission to download this app (or help to download it).

This is not a chat service. What happens when you try to download this app? Any error message?