Hello, 

As per your requirement, i would say that when you apply for registration again you need to check out in their offiial site all the details regarding getting a code of previous registration and then continuing the further process for attempting the exam.

Try logging in using your previous credentials itself. If you are able to do so, then no problem. Otherwise, you need to create a new one. However, no info is provided on website regarding this query. So, you can also call them and ask.

For more info https://medicine.careers360.com/exams/aiims-mbbs

Good luck