I have two cameras recording one on the road and one facing me, how do I put the one facing me in a box then the other in the background?

I have a Geekam 4K Action Camera, and I have that recording while I'm biking facing the front of my bike, So it can see the road, then I have my iPhone facing me recording me while I'm biking. I don't know how to put my face in a little separate box, and the video that I was taking on my Geekam Camera in the background. For example, the picture you see with pewdiepie in the little box down there, and then the video playing I want it like that, but instead of the green screen behind him, I just want the video on the iPhone in the box with the video from the Geekam playing on the screen. I have two cameras recording one on the road and one facing me, how do I put the one facing me in a box then the other in the background

Picture - in - picture.

When you start the cameras recording, CLAP. This will provide a "sound spike" in the visual representation of the audio.

Import the video into a video editor that can deal with multiple simultaneous video tracks. The freebies don't do that - I use Final Cut Pro. Sony Vegas can work…

At the start of the video, align the sound spike. The videos will be in synch.

Usually, the "main" video that fills the screen will be on video track 1. For the other video (your "picture-in-picture"), make that track 2. It will fill the screen until you scale it to whatever size you want. See if 20% works for what you need. You will also need to change the X-Y position to position it in a corner.