Kylo turns to the light when Vader’s mask is destroyed
I’m going to say the scenes we have seen with Rey, Finn, and Poe on a First Order ship take place early in the film. Maybe they are on some crazy mission to assassinate Supreme Leader Kylo Ren or are trying to sabotage or steal one of their Star Destroyers.
Whatever the reason, Rey ends up in Kylo’s meditation room with the charred and melted remains of Vader’s helmet. This obviously leads to a lightsaber fight between the two, which results in the destruction of the helmet.
At this point, Kylo feels the burden of the Dark Side leave him and falls to the floor in shock. Rey takes this moment to make her escape, as Kylo Ren is transformed back to Ben Solo. Solo then spends the remainder of the film without his mask and goes after Rey.
He feels remorse for all the people he’s killed, especially his father and also realizes his feelings for the scavenger from Jakku. That is why he follows her to Pasana and begins to work on getting her to trust him. He will want to be on her side and help her take down the First Order and Sidious.