Can not convert a BatchDataset into a Tensor or Operation

while I am trying to run this code, I am not able to perform self.img = tf.reshape(img, [-1,28,28,1]). I am getting this error -

TypeError: Fetch argument <BatchDataset shapes: ((?, 28, 28), (?, 10)), types: (tf.float32, tf.float64)> has invalid type <class 'tensorflow.python.data.ops.dataset_ops.BatchDataset'>, must be a string or Tensor. (Can not convert a BatchDataset into a Tensor or Operation.)