Olfactory dysfunction is a defining symptom of COVID-19 infection. Studies have demonstrated improved olfaction in patients with post infectious olfactory dysfunction after an olfactory training (OT). The aim of this study is to assess the clinical outcomes of olfactory training (12 weeks) therapy in the treatment of persistent olfactory dysfunctions after COVID-19. Specially, we aim to compare the effectiveness of two different olfactory training (different odors). A group will train themselves with 4 scents (rose, orange, clove and eucalyptus) and another group with 4 different scents (cheese, coffee, strawberries and lemon). Olfaction sensory evaluation will be performed by using different olfaction tests (Sniffin' Sticks and UPSIT) and complete questionnaires to assess olfactory perception and particularly parosmia and phantosmia.