The sense of smell is one of our most primitive senses, so a dream about a smell is usually about your basic instincts.
A dream that you smell an air freshener can be a sign that you instinctively feel that something in your life is dirty and you want to destroy it and replace it with something clean.
Some smells are connected with our past, for example there may be an air freshener that was used when you were a child so that when you smell its scent in a dream it brings back memories of those times. So, when interpreting this dream you would have to think about the connections you have with this particular air freshener.
Dreaming about an air freshener in general could symbolize a need to clear the air with someone, ie voice issues you are having or bring a friendship back on track.