Yes, you can withdraw ASBA bids. During the bidding period you can approach the same bank to which you had submitted the ASBA and request for withdrawal through a duly signed letter citing your application number, TRS number, if any. After the bid closure period, you may send your withdrawal request to the Registrars before the finalization of basis of allotment, who will cancel your bid and instruct SCSB to unblock the application money in the bank account after the finalization of basis of allotment.