How do I retrieve deleted messages that are on my iCloud

If you were syncing Messages with iCloud and deleted them, they can't be recovered. If you weren't syncing Messages with iCloud, do you have a backup you can restore from? Restoring from a backup erases all data currently on your device. Any data newer than when the backup was made will be erased. A restore is an all or nothing restore. You can't access a backup and only restore certain files.

Backup - Restore your device from an iCloud or iTunes backup.    *

ASC YouTube for how to restore an iPhone, iPad, or iPod touch from an iCloud backup

ASC YouTube for how to restore your iPhone or iPad from a backup on your Mac

Delete and recover emails in Mail on iPhone - Apple Support

If the mail is not in your trash, it’s gone,