There is no scientific evidence which suggests that tea is a proven cure or preventive measure for COVID-19 infections.
A fabricated post stating that drinking tea cures COVID-19 is circulating in social media; the post seems to originate from a statement made by Dr. Li Wenliang, who was researching the effect of tea and COVID-19. But he was an eye specialist rather than an expert on viruses. Hospitals in China are not treating COVID-19 patients using tea.
There are no medicines that have been proven to prevent or cure the COVID-19 and the World Health Organisation does not recommend self-medication to treat or cure COVID-19. The Ministry of AYUSH in its advisory has stated that drinking herbal tea or decoction made from Tulsi, Dalchini, Kalimirch, Shunthi, and Munakka once or twice a day can help boost immunity during COVID-19 crisis. But the ministry also advises that tea can be used to cure COVID-19. The Centre for Disease Control and Prevention (CDC) reports that there are no drugs or other therapeutics presently approved by the U.S. Food and Drug Administration (FDA) to cure or prevent COVID-19.
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19 including symptoms, prevention and available treatment, please refer to the World Health Organisation or your national healthcare authority.