Find unknown duplicate records

[naokichia]

I need to patch multiple records on click of a button. If there is more than 1 line of the same customer, it should assign to the same person who clicks it. However, the issue is the customer is unknown to the users and the app. Is there any formula to find patch duplicate record so that it can assign to the same person who request for it. 

The customer is not duplicated by accident. It refers to the different job request from them, however, we will need to assign the all job to the same person who click request job. 

ID	Assigned To	customer
1	A	ABC
2	A	ABC
3	B	XYZ
4	C	QWE