I need to retrieve a deleted text message from my iPhone.

one thing to check quick..

navigate to Settings > [your name] > iCloud, is the switch for Messages turned ON?

If so, your messages are not included in your iPhone backups

Backup methods for iPhone, iPad, and iPod touch - Apple Support

Sorry, but they are gone, if the phone was backing up to iCloud.

Apple is really serious when they ask if you want to delete the conversation.

It's a total shot in the dark, but if you have been backing up the phone to your Mac......AND.......the Mac has been backing up to another hard drive using the Time Machine application......it might be possible to try to find a record of the backup that might contain the messages.

Even if the backup can be found though, you will have to restore all the data on the phone to the time when the backup was made, so you lose any data on the phone since the time of the backup.