Just finish the three part Elseworld series.
"Elseworlds" ifeatures episodes of tThe Flash, Arrow, and Supergirl. The crossover began on December 9, 2018, with The Flash, continued on Arrow on December 10, and concluded on Supergirl on December 11. "Elseworlds" introduces the characters Batwoman and Lois Lane to the universe, as well Gotham City. In the crossover, Green Arrow, Flash, and Supergirl are drawn to Gotham City to confront Dr. John Deegan over his work at Arkham Asylum.
The conclusion of "Elseworlds" revealed "Crisis on Infinite Earths" as the next crossover, scheduled to air in late 2019.
I read the 10 part "Crisis on Infinite Worlds" comics years ago when DC seemed to want to clear up the not so popular characters and titles. I look forward to seeing what they will do for the TV special.