How to change the video viewing mode on the iPhone in two ways?
You can record a video with your iPhone positioned horizontally, vertically, or even upside down. If your iPhone is running iOS 13 or later, you can control the position of your videos in the Photos app, and if not You have iOS 13, you'll have to use iMovie, and here's how to do both.
How to control an iPhone through the Photos app?
Open the Photos app and choose the video you want to rotate.
Tap Edit in the upper-right corner of the screen.
On the right side of the toolbar below the video, click the Crop icon, which looks like a box with two arrows around it.
Next, in the upper left corner of the screen, tap the square icon with a curved arrow above it, and hold the button until your video rotates to the direction you want.
Tap Done at the bottom right corner to save the video in its new orientation.
If you don't like the results, you can always go back to editing and rotating the video to any other position.
How to Control an iPhone Using iMovie?
Open the Photos app and choose the video you want to rotate.
Tap Edit in the upper-right corner of the screen.
In the upper-right corner, tap the circle icon with three dots inside, select iMovie in the pop-up window, and the video will automatically open in iMovie.
Using two fingers, make a twisting gesture in the middle of the video, as if you are trying to rotate the video, rotate your fingers in the direction you want the video to rotate, and keep twisting until the video is rotated to the direction you want.
Click Done in the upper-right corner.
The video will be re-saved to your photo library to replace the original video, and rotate to the desired orientation.
If you don't like the results, you can re-edit the video and rotate it the other way to go back to the original orientation.