Hi Terry, here's a tutorial! https://www.mom4real.com/diy-air-freshener-plug-refill/
I always buy the cheaper refills and refill my old one. To do that you pull off the plastic tops and pour the fragrance into the bottle.
Here you go with a great video to watch.. https://www.youtube.com/watch?v=D9xyvG8PwKE
How do you insulate for winter an old uninsulated trailer home that has panelled walls?