How to clear Smartlist selection

Summary:

In workforce planning, for testing purposes, we have loaded Salary Rate and selected salary assumptions (col. E) as "Grade Unassigned" (row 1 in the screenshot). I am able to delete the salary Basic and Rate, but the system does not allow me to clear the assumption "Grade Unassigned".

I am aware that this is an out-of-the-box smartlist and does not contain #Missing to select, hence, it will not allow to delete directly or through a rule. Is there any way to clear the "Grade Unassigned" selection instead of creating a new smartlist including #Missing?