The concept of 'logging out' does not exist in Session.
Because we don't request any personal information, the way we create 'accounts' is not the traditional way. That means you don't set a username and password, instead, you are provided with a randomly generated Session ID and recovery phrase.
The only way to 'log out' is to remove the application from your device and delete all associated data. You can then only regain access to this Session ID via the recovery phrase. Warning: doing this means you will likely lose data like conversations and contacts.