How to get back to original tax return?

I submitted my state and federal taxes earlier in March and then realized I forgot to enter in a donation.  I received a letter from my state department of revenue stating that the return I had mailed was illegible or was in the wrong format.  I had already completed my amended return in preparation for sending it in once my original state return was processed but now I cannot get back to my original tax return documentation that I submitted before I completed my amended return.  Please advise on how to go back and get a copy of my original 2020 tax returns.  

 

Thanks so much!