The team has been working in a Scrum environment for a long time. They may not be a good “Scrum team,” but they are fine with how they are.
The optimal approach here would be coaching. Coaching techniques reveal opportunities for improvement to the team and also let the team members see their problems first. If the ScrumMaster starts with teaching and explaining, the team will most likely not accept it and reply that, as a self-organized team, they will decide how they work. The ScrumMaster is not there to tell them what to do. In some cases they refuse to accept such a ScrumMaster, and she has to leave eventually.