The amended state return form prepopulates state "refund received with previously filed 2024 return." I didn't receive a refund. Do I change it to zero?

You should not amend your return until the original return is processed.  

That is correct, the amended return is based on the assumption that you received the refund and that you are repaying it.  However, if the state catches the error before sending your refund you would not necessarily need to pay.  If they don't, you will.  So it is best to not amend until your return is fully processed.