Registration fields useless if user has account

Hello Tuan, the event form has as default the registration fields. We came to the situation that when users already have an account they get confused on when ordering of new events. As you can see on my print screen, the instructions are "If you have an account already, just enter username and the system will assign this registration to your account".

The complain is that they need to re-enter all the required fields again. Now if you login then most of the fields are pre-filled and this is what we want.

Can you explain what is the flow and functionality of these registration fields on the form and or how can we resolve the confusion with these fields on the position they are ?

Thanks,

Javier