I have Migrated from 2.2.0-GA to 3.0.0-GA.
In your online demo admin UI I have seen the custom field management option in the admin Console.but after migrating from 2.2.0-GA to 3.0.0-GA version in my local . I am not able to see those Custom filed changes option in my local admin UI .
I have marked the fields which is misssing in my local admin.

Thanks & Regards
Ankit Aggarwal