For that you have to change the case preference from the registration details which you can change twice a year and obviously before form fill up. So while filling up the form check the details you have provided and employ the correct option.

Now if you get a chance in SSC CHSL with the wrong caste then it will be of no offence if you get the job through UR category. If you get the job by your wrong caste then there can be issues of discrepancy or cancellation.

To know more about SSC CHSL visit the link below:

https://competition.careers360.com/exams/ssc-chsl

To know more about SSC CGL visit the link below:

https://competition.careers360.com/articles/ssc-cgl

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