According to the executive order by Russian Prime Minister Mikhail Mishustin dated 8 June 2020, Russian citizens are able to travel abroad to work, study, receive medical treatment or care for relatives. German government has also granted permission for foreign nationals to enter its territory in case of emergency medical care.
An official letter, confirming that you require treatment in Germany, is issued by the clinic and serves as authorisation for entry, if you have a valid visa. It is signed by the treating doctor and indicates the duration of stay.
If you do not have a valid visa, you are invited to lodge an application with the embassy by providing a standard set of documents together with a letter from the clinic. The application is usually processed within 5 working days.