I was covered under my parents ACA healthplan. The return is being rejected because I am missing 1095-A. I did not receive. What do I do?

It depends on whether you are also on your parent's tax return and if they received an Advanced Premium Tax Credit. 
This TurboTax Help article has instructions for the different situations.  You will need to coordinate with your parents to be sure your entries agree with theirs.  I'm on an ACA health insurance plan with my parents.

If you do not have time to speak with them today, you can always file an extension today with an estimate of your taxes based on the information you have already entered. That will give you until October 15th, 2022 to file the full return.  If you will owe taxes, you will want to pay an estimate of that now, so you will only on interest on any extra amount. If you pay too much, it will be refunded to you.  Please click here for a TurboTax Help article with information about  TurboTax Easy Extension found at the bottom of the left menu bar.  TurboTax Easy Extension