To select multiple values in one slicer, press ctrl key while selecting values in a slicer.

To clear all selections press the ‘Clear Filter’ button at top right of the slicer.

Clear Slicers in Dashboard
Clear Slicers in Dashboard

To change the name of a slicer, please right click on Slicer name and choose Slicer Settings. Then, change the Caption to update the name.

Change Slicer name
Change Slicer name