See if you have applied for the reservation and don't provided the Registration number, then also your reservation details is processed by the PGCET authority. So you will get the Reservation provided you must have the certificates required or else your admission will be canceled.

To know more about the Karnataka PGCET 2021, visit the link below:

https://engineering.careers360.com/articles/karnataka-pgcet-counselling

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