Need to remove the employee record from collector record

Hi Team

Version: R12.2.9

Business is using the Default Collector at customer profile class and that customer profile class assigned to most of customers (Multiple countries customers) account level in prod which Default Collect was not assigned any employee record in earlier.

As a part of Dunning Letters implementation, business wants to generate dunning letters for specific US country customers only and assigned new collector in place of Default Collector place.

But user has assigned the one of the employee records to Default collect window in prod wrongly which need to be removed but not allowing to remove and getting below error.