I have created a process model that allows assignment of requests to users. The

I am not sure if I am explaining my process correctly. Let me try again.
1. A request has been entered into the system
2. Project Manager comes along and decides to have John Smith work on the request. John Smith is a user in Appian and listed in people. So when the manager opens the request to assign it to John the Assignee field is blank until the manager starts typing it then displays a list of users that meet the criteria entered by the manager, who can select someone (John Smith). The request is assigned to John.
3. Another request comes into the system that is of a higher priority than the request that was assigned to John. So we want to assign this request to John and un-assign the other request.

The problem is once John's name is in the request it can only be removed by entering someone else's name. I would like to be able to make the assignee field blank (meaning unassigned).

I am not sure if I am explaining my process correctly. Let me try again.
1. A request has been entered into the system
2. Project Manager comes along and decides to have John Smith work on the request. John Smith is a user in Appian and listed in people. So when the manager opens the request to assign it to John the Assignee field is blank until the manager starts typing it then displays a list of users that meet the criteria entered by the manager, who can select someone (John Smith). The request is assigned to John.
3. Another request comes into the system that is of a higher priority than the request that was assigned to John. So we want to assign this request to John and un-assign the other request.

The problem is once John's name is in the request it can only be removed by entering someone else's name. I would like to be able to make the assignee field blank (meaning unassigned).