video editing software recommendation
The way this is usually done is either by recording the screen at full resolution and zooming out the footage until you want a close-up, or by using a screen recorder which allows you to zoom in as you're recording.

But if you already have footage, any decent editor should allow you to zoom in. Just know that zoomed-in footage will be at a lower quality than recording at the full resolution and cropping.

If you're on Windows, you can try Adobe Premiere or Sony Vegas. There are probably others, but those 2 are fairly popular.