Unable to update database Flask-SQLAlchemy Model

Question

I have a challenge updating table fields in the database using Flask-SQLAlchemy models. When I call the update endpoint, it does not update the database I have a small model for user as follows

User Model

class User(db.Model):
   id = db.Column(db.Integer, primary_key=True)
   first_name = db.Column(db.String(80), nullable=False)
   last_name = db.Column(db.String(80), nullable=False)
   password = db.Column(db.String(120), nullable=False)

   def save_to_db(self):
       db.session.add(self)
       db.session.commit()


   @classmethod
   def update(cls):
       db.session.commit()

   @classmethod
   def find_by_id(cls, id)
           return cls.query.filter_by(id=id).first()

User Resource

class UserResource(Resource):
    @jwt_required
    def put(self, user_id=None):
       user = User.find_by_id(id=user_id)
       
       if not user:
           return { 'message': 'User not found' }

       user.first_name = 'foo'
       user.last_name = 'bar'
       user.update()
       
       return { 'message': 'user updated' }