For SSC GD there are no correction window available. So you can't edit the details once you have submitted fully. You can appear for the examination, but during document verification (laterwards) there can be problem due to the discrepancy in the roll number.

For a last try you can contact the regional office i.e., if you are from Westbengal then it would be Eastern Region. If there are any procedures to change it then the officials may guide you out. Although this possibility is very less.

To know more about SSC GD visit the link below:

https://competition.careers360.com/exams/ssc-gd-constable

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