National Center for Complementary and Integrative Health and the WHO has stated that chemicals found in tea do not cure COVID-19.
Methylxanthines are a group of chemicals which include caffeine, theophylline, and theobromine are obtained from plant secondary metabolism. They are found not only in tea but also chocolate and coffee in different concentrations.
A news release by NCCIH (National Center for Complementary and Integrative Health) states that there is no scientific evidence that tea and other herbal therapies would prevent or cure the illness caused by the coronavirus. Similarly, the World Health Organisation states that there is no specific medicine to prevent or treat 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.