Wait 3 years after basically shutting the doors down and you too can have an A rating once again.
Funny even the document you posted proves this. Section "Reason for Rating".
Length of time business has been operating.
Since they were next to doing no business at the time this business memo was put out (2014) and had not been doing much business for over 3 years (3 year limit on complaints), the score by default raises.
Last known rating of Trump University (not some phony Trump made up form years after the fact) is this screenshot from The Wayback machine.
https://web.archive.org/web/20100420184236/http://www.bbb.org/new-york-city/business-reviews/training-programs/trump-university-in-new-york-ny-97075/
We also can confirm that D- rating with two news reports (NY Times and Washington Post) that covered the rating in 2011 (year the University was about wound down...ie closing). (I am too lazy to hunt the liberal news links down right now, but if you google Trump University and Fact check they have the articles linked if you want to read them yourself). At factcheck.org article.