It is easy to overcorrect when introducing something new into your service, either saying nothing at all and letting the fragrance speak for itself, or overselling it in a way that makes a genuinely simple addition sound like a big deal it does not need to be. There is a comfortable middle that works better than either extreme.
Mention it in passing, as part of describing the full process, rather than as a separate pitch. Something like: we finish every detail with a cosmetic-grade fragrance; it's non-toxic and lasts a few weeks, said the same way you would mention any other step in the process, no different in tone than describing the wax or the interior treatment.
If a client reacts positively, that is your cue to say a little more, not a cue to keep pushing. Answer their specific question, mention the scent by name if they ask, and let their curiosity guide how much detail you give rather than delivering a script regardless of their reaction.
If a client does not react at all, that is fine too. It does not mean the addition failed. Most people do not comment on most parts of a detail out loud. The fragrance is still doing its job for the next few weeks whether or not it gets a verbal reaction in the moment.
The goal is not to sell the fragrance. It is to mention it naturally enough that it reads as a genuine part of your standard, not an upsell you are trying to talk someone into.