Yes of course, you can add a minor nominee. 

When you add a minor as your nominee you need to provide the details of the guardian along with the nominee details. Moreover, the account holder cannot be the guardian.

To add or edit a nominee to your Arihant Capital account, you can go to the ArihantPlus app, go to My Account and Profile section and tap on Nominee Details. You will find an "Edit" button on top and update your nominee details there. You can also go to https://erekyc.arihantcapital.com/ and update it from here if you do not have .