I had the same problem. It would not let me no matter where i did it. If you can, you would need to view this official website in your browser as the desktop version. How to do this varies based on your phone and browser. Then once on the site and logged in you can manage your profile/avatar. I got fed up with trying on my phone and just used my laptop.

Just switch to PC for it as it's way easier then.

Not all phones support file upload, so you're really better off using a desktop PC or laptop for that.

I couldn't upload on my phone or laptop. :_;

Commander Ange; bringing you my life, liberty, and property.