How do I change my Apple community avatar pic

That is done in your profile, however you have to have a higher level to get the ability to have a custom avatar.

See this. Learn, share, and get awards in Apple Support Communities

• Click on your name at the top of this page.
• Click on "Change photo and avatar"

Be helpful to other users, especially by responding to new posts. See: Learn, share, and get awards in Apple Support Communities

Isn't it nice when you get two answers and they agree 😉