Retrieve deleted texts from iphone6s

You would have to restore your device from a backup that was made before you deleted the messages:

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

Just be aware that restore is an all or nothing process. You cannot just restore text messages (for example) and any information between now and when the backup was created will be lost.

If you have a backup that contains the deleted texts you can restore your iPhone from your backup and get them. You will lost anything you did after the date of that backup.

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

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

Note that a restore will replace all data on your phone (not just texts) with the data from the time of the backup.