how can I install Qt Designer for PyQt5.
I installed SIP from PyPi by running: 
    pip3 install SIP
and I installed PyQt5 also from PyPi by running: 
    pip3 install PyQt5
but I didn't find QT Designer
Qt designer doesn't come bundled with PyQt5. You can install it separately using pip install pyqt5-tools (or pip3 install pyqt5-tools).
You will find designer.exe at:
...\Lib\site-packages\pyqt5_tools\Qt\bin
how can I install Qt Designer for PyQt5 for WINDOWS 10