How to get deleted text back

I don't think you can unless there was a backup stored before it was deleted

You can find out how to restore from a backup here - https://support.apple.com/en-us/HT204184

How to back up your iPhone, iPad, and iPod touch - https://support.apple.com/en-us/HT203977

Other than that, there isn't another way.

You can not recover a deleted text message easily, I'm sorry.

The only way is to erase your phone and restore a backup which has the text message saved - the question is do you have a backup which would have included the text message?