How to access a video file that an app is hiding
Most likely you can see it only from within that app: the file will be stored in the app's "private" directory where only itself has access to (unless you use "root powers"). See my answer here for details.

Even assumed you'd manage to extract the file (e.g. using root powers) and transfer it to your laptop, you most likely won't be able to watch it: those applications normally use DRM (see these questions for details), and their media files are encrypted.

Without knowing the identity of "this app", it's hard (or rather impossible) to say anything more specific.