The only thing that comes to

The only thing that comes to mind is that video records audio at 48K while a Zoom defaults to 44.1 so make sure that it's set to 48K for future use.

What editing software are you using?

Some software allows you to slow the audio to match the video and, more importantly, keep the pitch correct.

If yours doesn't, try Audacity (it's free) as it lets you do this.

Mike