I made a mistake while filling up the CAT 2019 application form. In other personal details- Serial/Entry no of cast/tribe. I mistakenly put the the wrong serial no. Will they reject my application form or this blunder can be rectify in correction window

Because this comes under Category field, the regulations are not quite clear if you can correct them during the correction window. What we would suggest you is to reach out to the helpdesk at cathelpdesk@iimcat.ac.in. Alternatively, you can also raise Candidate query on the official website. They would suggest you the best course of action.