That is a helper function supplied in the local util.py file that should be imported at the bottom of the first code cell
import keras
import json
import numpy as np
import pandas as pd
import nibabel as nib
import matplotlib.pyplot as plt
from tensorflow.keras import backend as K
import util
Take a close look at the first cell I attached above. Notice the line
import util
That’s how. That code cell needs to be executed or ‘run’ before anything else in the notebook. That line makes the functions in the util.py file accessible to the namespace. If that import line fails it means that python file is missing from the workspace and it needs to be refreshed. There are other threads and FAQs that cover how to do that.