The choir belted out a powerful rendition of "Stand by Me," which brought many viewers in the virtual audience -- who could be seen watching on a wall of screens behind the judges -- to tears.
"That was incredible," Thompson said after the performance. "I don't know if you get a kick out of making people cry their eyes out, but that's what you guys do every time you hit the stage... That was amazing, thank you."
ET's Kevin Frazier spoke with Klum after Tuesday's show, and addressed the possibility of Cowell returning to the show for the semi-finals in a few weeks.
"Let's give him another minute," Klum said. "He's had about a half a minute. I mean it's been one week and he's already at home, I think that's absolutely incredible. So, you know, I would say let's give him another week and let's see how far he is then."
Mandel, meanwhile, said he missed Cowell being behind the judges' table, but added, "I know for sure she is watching the show."
Cowell underwent a six-hour surgery, which included having a metal rod placed in his back, after an electric bike accident at his Malibu, California, home. ET learned last Tuesday that the 60-year-old judge is walking again as part of his recuperation.
On Monday, ET also learned that Cowell was happily back home and doing well. For more on Cowell's recovery, watch below.
America's Got Talent airs Tuesdays and Wednesdays at 8 p.m. ET/PT on NBC.