The number one tool in a Scrum Master's Kit is the Scrum Guide. The Scrum Guide is not a hard defined rule that all teams must follow by the book.
Scrum isn't a rigid process. In fact, Scrum is more of a framework than a process. If Scrum was a rigid process, it means that all teams will have to implement Scrum the same way, and that's not possible. No two teams are the same.
Scrum is very flexible, and that's why a team of 5 people in a startup and team of 50 people in an enterprise can implement Scrum successfully, and achieve their goals.
Think of the Scrum Guide as a skeletal structure that can fit into different body types. It's a guide book, not a rule book.
Listen to this podcast on "what to do on your first 90 days of a scrum master for a new team