It's on the show's website, but somewhat hard to find. On the FAQ page under What is the performance schedule?:
Adrienne Warren will perform as Tina Turner Tuesday through Saturday evenings and Sunday matinees. Nkeki Obi-Melekwe will perform as Tina Turner on Wednesday and Saturday matinees. Nkeki Obi-Melekwe will also perform on Sunday, November 24th, December 22nd and June 7th. Due to the nature of live theater, we are unable to guarantee the presence of any particular cast members at a specific show.