How to create an app icon from scratch, generate the required sizes, and add to your iOS app.
Image editing - Figma is a free online design tool used in the video. You can use any design tool you like, such as Photoshop, Sketch etc, as long as the output is a 1024x1024 .png image.
Asset generator - Iconizer is a free mac app for generating the correct sized assets from your icon.