Once they dry out they are dead and cannot be refreshed, throw them out and just use the oil or a spray in the air or wipe a little of the oil on your surfaces

I have dried eucalyptus hanging around my house that has lost its smell. I've heard spraying a mix of eucalyptus oil and water refreshes them. However when I went online to purchase some I see there are multiple types...anyone know what type of eucalyptus oil is the right one? I dont want my house smelling like a big cough drop. Thanks!