Payload update add new field to array or anywhere

Suppose you want to chage something at payload.test.address[0] record….

%dw 2.0
output application/json
---
payload update 
{
   case .test.address[0] -> your implementation here
}

helpful references https://medium.com/@shruthi_r/update-function-v-s-operator-in-dataweave-4aa9f2ab41cd