Backpropagation in cnn, how to train a filter on input?

Question

Neural networks

Please tell me, for example, the numbers in the photo, how to determine the delta for the filter.
The delta of the filter in front of a fully connected network is clear, but I don’t know how to calculate those filters after it as a delta.
This network without pooling

Photo look from left to right (filters are calculated, a fully connected neural network)

Then from right to left (error calculation, updating weights)

I don’t know how to train a regular ns, but here is the problem (

Answer 1

Reverse convolution of the original image.