Scripts

PlayDialogScene -- function to launch the video.
After completing the task, set a trigger: Trigger(OBJECTIVE_STATE_CHANGE_TRIGGER,...
In general, it's not difficult; it's largely similar to the region-based method from the neighboring topic.

How do I insert my own voiceover? I have the necessary format, but I can't insert it into the dialog scene. Thank you in advance!

You need to export the sound as a resource into the game. And in the video, insert this sound (or sounds). In general, it's not a trivial task; you can get a partial understanding of it here: http://psatkha.narod.ru/tutorial_ru.html. I'm not sure if it's worth the effort; it's practically impossible to adequately voice over videos at home, and then you have to struggle and learn how to insert them.