Go back to 9.3.3?

I have a minor crack in my 6s+ screen which I took to the Apple Store for repair. I have iOS 10 beta 4 and they said I needed 9.3.3 to repair. He also said they usually can do that but their servers were down. He said I could do it myself and then bring it back for repair. How do I go back to 9.3.3?