Thanks to Aiden for the heads up.
According to the official description, Jay Garrick plays a role "in a pivotal flashback episode" that establishes "the Golden Age Flash as a member of Earth-2's Justice Society of America." Per the CW, this miniature crossover will "officially bring Stargirl [Brec Bassinger] into CW's post-Crisis CWverse alongside The Flash, Superman & Lois, Batwoman, Black Lightning, Supergirl, and DC's Legends of Tomorrow."