The CW has released an official description with spoilers for the Monday, April 23 episode of Supergirl.
The title of the episode is “In Search of Lost Time” and here’s how the network describes it:
J’ONN HAS TO FACE THE TRUTH ABOUT HIS FATHER – When Myr’nn (guest star Carl Lumbly) inadvertently causes psychic disturbances at the DEO, Supergirl (Melissa Benoist) must work with J’onn (David Harewood) to contain the resulting chaos. Meanwhile, Mon-El (Chris Wood) begins training Kara in fighting techniques he’s learned in the future for battling Worldkillers. Andi Armaganian directed the episode with story by Eric Carrasco and teleplay by Katie Rose Rogers & Nicki Holcomb (#315). Original airdate 4/23/2018.