I have an app icon for iOS but Apple doesn't allow alpha to be in the image. How to remove this alpha channel? I only have the png image with me I don't have the source file as my friend did the image for me.
Assuming you don't have another image editor, then you can open it in Preview on your Mac, and use the Export option to resave it in a different format- to ensure you get rid of the alpha channel, it might be best to export to JPG (best quality), then open that and export it as a PNG again.
Having said that, I suspect you're probably OK submitting an icon with a transparency channel as long as there's no actual transparency.