I have posted about this before - my husband’s home health care nurse lost her sense of smell for about 6 months due to covid. She purchased a ‘smell test kit’ on amazon and within a couple of weeks, her sense of taste and smell slowly started coming back. Here is the link to the one she purchased.
My cousins had it, and diffused/sniffed eucalyptus lavender essential oils. Got their sense of smell back in about 2 weeks.
Be aware, Eucalyptus is highly toxic to some pets, especially cats, and essential oils should not be rubbed directly on your skin, without a hefty dilution of a carrier oil.