Problem with encrypted backup using iTunes on my Mac

Hello all,
I have had my iPhone six plus now for a year and a half. I am going to be switching my carrier to T-Mobile so I am going to get a new iPhone 7 plus. I went to do an encrypted backup on my mac using iTunes and for some reason it is acting like I have already created a password for an encrypted backup. As far as I know I have never done this. Is there a way to recover this password and if not is there a way to reset it so I can start over?

Thanks,
Greg Wocher