If you want refund then there are two criterias :-
First if you opt for seat withdrawal, then the fees will be refunded after deducting the JoSAA processing charges of Rs. 2000 (as per josaa 2020 brochure).

Second - if your seat is cancelled due to not meeting the eligibility criteria or fault in the uploadeded documents, then the fee will be refunded by deducting Rs. 2000.

Now if you have already accepted the seat allotted by JoSAA 2020, then you can withdraw the seat by reporting online starting from the 2nd round and upto the 5th round of seat allocation (before the last round of seat allocation).

I f you want to withdraw your seat, then you must do it before the starting of 6th round counseling.
Because after that, you will not get refund if you want to withdraw in final round ( as per josaa 2020 brochure).

Yes, you can surrender the seat allotment before Round 6 at some minor deductions, particularly the registration fee of 1500, but the rest 33500 I believe is refunded. But do decide wisely before making the choice as it cannot be reverted.

For more information on JOSAA rules and regulations do refer the link below

https://engineering.careers360.com/articles/josaa