Hi

Sorry, but you cannot change any of the locked filled choiced. JoSAA 2019 gave 5 days to fill and finalise every choice you had filled in. That's it. No student will be further given any more time to change the locked choices. You cannot change the result you will get in the subsequent rounds. To avoid inappropriate or undesirable filling of choices, JoSAA Counselling conducted two Mock Seat Allocations and had given a span of 5 days to check and recheck. 

You can always check the same about JoSAA Counselling 2019 in a greater detail through this link: https://engineering.careers360.com/articles/josaa-counselling.

Best of Luck. 

Hope this helps.

Cheers!