How to change the unread messages that Apple has read?

Cannot be changed. Only the unread SMS of Apple can be changed to read.

First, enter the information interface of iPhone, and unread messages will be displayed first. Click the edit button in the upper left corner to enter the editing interface.

Secondly, find the "Read" button in the lower left corner and click.

After clicking this button, all unread messages will become read. If there is a lot of unread information bothering you, you might as well use this method to solve it with one click.

Extended data:

IMessage information is text, photos or videos sent to another iPhone, iPad, iPod touch or Mac through Wi-Fi or cellular data network. This information is usually encrypted and displayed in blue text bubbles. To turn iMessage messages on or off, go to Settings > Messages.

If you don't use iMessage information, you can use SMS/MMS. These messages are texts and photos sent to other mobile phones or other iPhone, iPads or iPod touch. SMS/MMS is unencrypted and appears in a green text bubble on the device.

References:

Apple official website-About iMessage information and SMS/MMS.