If you want to switch a role to unnamed, it cannot have any time cards or cost cards associated with it. If there are cards, reject and delete them.
Once the role is "clean," edit the role. From the Role Booked Resource Tab or Role Requested Resource Tab (depending on whether you want to book or request an unnamed resource) click the Add Resource Candidates button. Select at least one of the following:
- Cost Center
- Location
- Title
Click Query.
Right click Unnamed and choose Set Preferred Resource.