A Gaussian filter in image processing is also called Gaussian blur and is a low-pass filter.
You can apply it on your images to blur them, if you think it might be beneficial for the training.
It’s not the same as Gaussian noise, which is usually additive noise to the input signal.
You can also implement the Gaussian filters in a conv layer, but depending on your use case you might want to use PIL methods to add the blur to the images.
Where did you read about these filters and did the source explain where and how these filters are applied?