@Rohit Parmanandka first of all i assume you have a Minors demat acc opened with Kotak Bank. If not, then get Minors pan and then open a minors savings account and then demat account.
After that register your minors beneficiary by filling form at Kotak bank (they will guide you).
After the beneficiary is registered, got to ipo section in mobile banking or net banking and check/verify beneficiary details.
Main thing should be that minors name is thare with his/her pan details.
Dont call customer care, as all ths stuff is alien for them.