To set a slicer variable filter:
Click Slicer on the Section title bar to open the Slicer pane.
Select a member from a dimension in the Catalog pane and drag it to the Slicer pane.
Every dimension folder contains a members subfolder named Values For Domain, which contains the members that are eligible for selection in the Slicer pane.
Select the member(s) you want to use as a variable filter and click OK.