Question block fields can be configured to hide once a user has completed them and their answer is validated.

Go to your Site.

Click Competitions in the menu

Then for the desired competition, click hen edit the flow

You'll see something like this

On the co-reg page, toggle the question block questions to 'Hide' once answered.

That's it.

Now go Publish your site to see that changes live.

For information on how you can customise this, please refer to the event documentation sb.Events.HIDING_QUESTION_BLOCK_QUESTION