How do I add an external package to my Python file while creating exe using pyinstaller

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Windows

Python

Let me take an example.
I make an automation script using pyautogui and i want to make my .pyw file a standalone application and run it on computers which do not have python preinstalled.
Now i go to the command prompt and type :pyinstaller auto.py
which gives me an error.
So how to i include the pyautogui in my exe file.
Thank you.

What I have tried:

As previously written ,i opened command prompt and typed
pyinstaller auto.py