How do I retrieve deleted messages?

IF you have not activated iCloud Messages and IF you have these messages backed up you can restore your iPhone from your backup. You will lose any data added since the date/time of that backup.

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Read the Apple Recommended response above that was posted by deggie and that will tell you what you need to do.

I deleted a conversation with someone how can I retrieve it back

I just deleted 1 message with many photos by accident

I am looking for the last new message just sent with many photos