If you want to change the aspect ratio of a photo taken by your iPhone or iPad you can easily do so through the Photos app. Select the photo you want to change and tap Edit in the top right corner.
It used to be that if you wanted to do any video editing aside from trimming, you'd have to pull your video into iMovie or a third-party video editing app. With iOS 13 that is no longer the case - the updated operating system makes just about all the photo editing tools available for videos as well. Now you can adjust the contrast, brightness, saturation and more, add filters, crop, rotate, straighten and mute audio all from the Photos app.
Apple has updated iPhone's photo editing interface in iOS 13, making it more intuitive and adding a few new features and tools as well. You can now fine tune filter intensity, flip photos, and adjust their perspective along the x and y axes. Flipping a photo simply gives you a mirror image while adjusting the perspective along the horizontal and vertical planes basically lets you adjust the viewing angle, similar to Instagram's perspective correction tools. Here's how to do both on iPhone: