A bank account holder might want to add or change a nominee for its account for several reasons viz. existing nominee died, dispute with existing nominee, prefer to add a different person as nominee, changing nominee because of a mutual understanding, etc.
The banks generally take the nomination details during the opening of a new account, which can be changed by the account holder as and when he likes. If the nomination details are not added in the beginning, then it can be added at any point of time later.
To add a nominee or remove it, most of the banks have a specific application form for it. You can enquire about it at the branch office of the bank, fill in the details and submit there. Some of the banks might not have a specific form for it, where you have to submit a written and signed letter for such addition and deletion of nomination details.
The following formats would be good enough for this purpose. They are only for your reference.