In Workshop you can use the Event to “Reset ____ variable” on a button group to reset the desired variable values, you can add as many events as you want to a button to do this with the variables you want to reset!
See an example configuration in the attached screenshot
Specifically for static option sets, one solution is:
Make a new object table (can be on a new, hidden page)
Toggle off: Enable auto-selection. Note the name of this table’s auto-generated active object.
Reset the new active object variable with either an event or by saving and refreshing
Create a button with an event to Set variable value where Source variable is the temporary active object variable and Target variable is the one whose default you want to clear.
Save with current defaults.
Clean up and delete the temporary button, object table, and active object variable used here.