It seems like you used godot? If you use dialogic too, you can add a variable (i.e. "dialog2completed" or something) and set it at the end of the dialogue and also add an label there. Then you can either check at the begin of the dialogue if the variable is set, if not you can jump to the label you created at the end or check it in code before you call Dialogic.start("...").
As an alternative without dialogic you can use an autoload-class where you create a variable and check this before you start the dialogue, this way it won't get overwritten when you reload the current scene, because it is saved outside of it. There are probably more ways to do it, you'll figure something out ;)