In climactic scene of The Nun, Valak possesses Sister Irene's body while trapping her in a star marked shape in the cellar. While The Nun is chock-holding Frenchie, he manages to grab the orb containing Jesus's blood, which Sister Irene is wearing & manages to cast out Valak, thus freeing Sister Irene for the time being.
What did he do that made Valak leave Sister Irene's body. The orb was still intact so he couldn't have had Jesus's blood on his hands to make Valak leave. The orb itself isn't effective as Sister Irene is possessed while wearing the orb.
So what did he do?