Yes you are eligible to participate in phase 3 of NEET MBBS counselling in Andra Pradesh,even if you were alloted a seat earlier.

If you joined and reeported to the previous seat, you can still attend phase 3 to upgrade .If you didnt report, you are still allowed to participate ,but you wont get the same seat again.

Andra pradesh neet counselling website : drntr.uhsap.in (http://drntr.uhsap.in)

make sure you are following the official website for phase 3 schedule and be ready with your documents .this is your final chance to secure or improve your seat.

all the best!