You will get the roll number from the hall ticket of the board you have completed your 10th. Also keep in mind, that you must be very sensitive while filing the form because any mistake in the form may create trouble for you. So enter the information very sensitively.

To know more about NEET phase 2 Application form visit the link below:

https://medicine.careers360.com/articles/neet-application-form

I hope this answer helps. All the very best for your future endeavors!