How do you zoom in on video clips/images without changing the scale?

So in my video, I have my laptop out, and I'm trying to edit a separate video onto that laptop screen as if it were playing. I can vaguely get the size of the video to fit the screen, but I want it to fit more precisely. How would I zoom into my background clip without changing the scale size? I've tried searching it up, but all I could find were videos on how to pan or zoom in, which isn't what I'm looking for. All help is appreciated. Thank you.