I am trying to use the VGG16 architecture available in the Wolfram Neural Network Repository to classify the Fashion MNIST dataset. The VGG 16 by default accepts images of size 3x224x224. However the images in the Fashion MNIST are grayscale of dimensions 1x28x28. I have tried to tune the model by using the command

newNet = NetReplacePart(vgg16, "Input"->NetEncoder[{"Image", {28, 28}, ColorSpace->"Grayscale"}]]

But this throws an error message that says

NetEncoder producing a 1x28x28 array of real numbers cannot be attached to a port Input which must be 3x224x224 array of real numbers.

This is highly frustrating and I cannot find a way through. Any help will be deeply appreciated. Thanks in advance.