The Black Cats have suffered back-to-back relegations, finishing in bottom place in both the 2016-17 Premier League season and the 2017-18 Championship season.
Sartori believes that the club can regain their place in the top flight but insists that this will take time.
Speaking to CNBC, the Uruguayan said: "I think 17 months ago it was a club in the Premier League, now it's starting the League One season so definitely something went wrong there, something went very, very wrong.
"The biggest job we have to do now is to identify what are the problems and then a very strong turnaround to take the club back to where we believe it deserves to be, and most of the fans, which is back in the Premier League.
"We have a plan which is a two to three-year plan which is very aggressive and is actually working pretty well. From a business point of view, it's turning and showing the results of the job we are doing."
Jack Ross's side currently sit in fourth place in the League One table and will play Rochdale at the Stadium of Light on Saturday.