Finding matching Values in Column A and from those values highlight duplicates in another column

[HelpmeExcel123]

I need to locate all duplicate values within each set of ID numbers.

I know how to find duplicates in one column, but how can I base it on matching ID's over and over?

 

[hagia_sofia]

Hello, I am not sure if I understand it correctly - is it supposed to be something like the following?

=COUNTIFS(A4:A42,A4:A42,B4:B42,B4:B42)