TFF : change the code have no effect in changing test accuracy values

To improve this tutorial and test other things, I was pretrained the network with a centralized way in EMNIST database. Then I would like to Fine tune the pretrained network with a federated code above. So, I only added:

def create_keras_model():
  return tf.keras.models.Sequential([
      tf.keras.models.load_model(path/to/model, compile=False)
      tf.keras.layers.Dense(10, kernel_initializer='zeros'),
      tf.keras.layers.Softmax(),
  ])

The problem is that I find same test accuracy values compared to test accuracy values without fine tuning a pretrained network. Can you please give me solution.