The singer was on Team Kelly during a previous season, but returned for season 23 in a trio.
The anticipated Showtime drama will return on March 24.
The band also played "What Happens After You?" on Tuesday night's show.
Trey Louis was in the building during the 2018 Santa Fe High School mass shooting that killed eight students and two teachers.
Smith gave no information as to what they were doing on set.
The 'Game of Thrones' prequel has begun production on its second season
Among new wrinkles are: "Playoff Pass" and return of the Playoffs.
The host announced his move on Thursday's show, where it was revealed that Ripa's husband, Mark Consuelos, will replace him.
Boss, Ellen's DJ and TV partner, died in December at age 40.
The country legend said she was the first one approached for Shelton's spot 12 years ago.
