Don't worry you can download your hallticket for AP EAMCET 2020 without the registration number and then find it from the hall ticket.
You can download your hall ticket by entering your registered mobile number instead of registration number.
You can find your registration number at the top right of your admit card above the hall ticket number.

Download hall ticket from this link https://sche.ap.gov.in/EAMCET/Eamcet/EAMCET_GetPrintHallticket.aspx