Inclusion Criteria:  Adult out-patient (≥18 years of age) Previously diagnosed with coronavirus disease 2019 (COVID-19) by laboratory confirmation using reverse transcriptase polymerase chain reaction (RT-PCR) for the detection of severe acute respiratory virus coronavirus 2 (SARS-CoV-2) Complaints of persistent olfactory disturbances, subjectively  Quantitatively documented to have olfactory dysfunction by  Butanol threshold test (BTT) Smell identification test (SIT) All subjects give written informed consent Subjects must be available to complete the study and comply with study procedures.  Exclusion Criteria:  Inability to comprehend and to follow all required study procedures Allergy or severe reactions to the study drug or smell training Pregnant or breastfeeding women Pre-existing factors which may account for persistent olfactory dysfunction besides COVID-19 (e.g. nasal polyps, obstructive lesions within the nasal cavity, severe anatomical malformations…) Received an experimental agent (vaccine, drug, biologic, device, blood product, or medication) within 1 month prior to recruitment in this study or expect to receive an experimental agent during this study. Unwilling to refuse participation in another clinical study through the end of this study. Have any condition that the investigator believes may interfere with successful completion of the study.