iCloud issue

There is no option to do that. If you don't have iCloud Messages turned on but do have an iCloud Backup, you can erase your iPhone and use the backup to do a complete restore but you cannot otherwise view the contents of the backup.

Also note that messages are included in iCloud Backup only if iCloud Messages is not turned on. See: What does iCloud back up? - Apple Support

If you have iCloud Messages turned on and you delete a message, it is gone. Also see the information in Use Messages in iCloud - Apple Support including the following:

When you turn on Messages in iCloud, your message history is updated automatically on all of your devices. That way, you always have the same view everywhere you use iMessage. When you delete a message, photo, or conversation on one device, it’s removed from all of your devices. And since all of your attachments are stored in iCloud, you can save space on your device.

See the following from Use Messages in iCloud - Apple Support

You can use Messages in iCloud on your iPhone, iPad, iPod touch, Apple Watch, and Mac. For your privacy, Messages in iCloud is end-to-end encrypted, which means you can't view or access Messages online via browser.