I have a pre-owned Phantom 3 standard but unable to delete the previous owner info ...all my flights are on my and his

If you are talking about the flight records in the app just swipe left on any you want to delete.
If you are concerned about the internal data recorder, don't worry because after you fly a few times you would have overwritten any older records there.

Hi Kevin, the flight records of the pre-owner can be deleted from the APP directly. Just slide the flight records left to delete.

I tried that and it deleted from both accounts