You can execute the the following steps.
1) Please remove the screws first.
2) Then open the cover of the box and loosen the nut indicated in the picture.
3) Then pull be the valve apart from the box.
4) Remove the two screws in the corners. They are very small, so keep them in a safe place.
5) Then gently pull the moving part out.
6) Then clean the inside of the black unit. Please do not use brute force to clean it. You can let some water flow through.
After that, you can assemble the valve following the steps backward.