How to add default dependent values to an existing independent valueset

Hi,

I've and independent value set Account in Chart of Accounts and a value set sub-account dependent of Account value set.

When I'm creating a new account, my sub-account is automatically defaulted to a default value '0'.

However, I have n number of accounts already existing (created before the sub-account value set created) which does not have default values.

If I have to populate default sub-account values  to all those account codes, is there any way to do so automatically?

Regards

Bhavesh