For SSC you need to have a valid EWS certificate during the application period, So as you have the EWS certificate which is valid till March 31, 2022 & the application process is with in March then you are eligible for the EWS. During the correction process, if the option is available you can change it. The options that will be available in the correction process isn't mentioned in the official notification of the SSC CHSL 2022.

So wait for the moment, and see if the options are available.

For more information regarding SSC CHSL 2022 you can consider the link below:

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

I hope this helps. Wish you a great day!