Due to the differences with a web application vs a desktop application, drop down selection fields via RI (such as Priority, Workorder Status, User, etc) have a couple different ways of accessing depending on your device.
Drop down selection
Select the control 
to drop down the list of available selections for this field.
You also can just type in two periods and the drop down selection will show
Existing drop down selection removal
To remove an existing selection, either select the 
which will then populate the selection field with the -
Or select the -
