SRM MDM Import scenario

Hi,

I am sending data from ECC to MDM with price and contract as qualified lookup tables. In import manager, I have a key combination of fields A+B+C+D. Now, If i change filed A in ECC and send data to MDM, it is creating new record in MDM. However, the MDM record should be updated. Please let me know how this can be achieved? I want combination of A+B+C+D as key field.

Regards,

Rajeev