I was able to create the path and install pyinstaller appropriately.
C:\Users\Ankit.Aggarwal>pip install pyinstaller
Requirement already satisfied: pyinstaller in c:\users\ankit.aggarwal\appdata\roaming\python\python36\site-packages (3.4)
Requirement already satisfied: setuptools in c:\program files (x86)\microsoft visual studio\shared\python36_64\lib\site-packages (from pyinstaller) (39.0.1)
Requirement already satisfied: pefile>=2017.8.1 in c:\users\ankit.aggarwal\appdata\roaming\python\python36\site-packages (from pyinstaller) (2018.8.8)
Requirement already satisfied: macholib>=1.8 in c:\users\ankit.aggarwal\appdata\roaming\python\python36\site-packages (from pyinstaller) (1.11)
Requirement already satisfied: altgraph in
c:\users\ankit.aggarwal\appdata\roaming\python\python36\site-packages (from pyinstaller) (0.16.1)
Requirement already satisfied: pywin32-ctypes in c:\users\ankit.aggarwal\appdata\roaming\python\python36\site-packages (from pyinstaller) (0.2.0)
Requirement already satisfied: future in c:\users\ankit.aggarwal\appdata\roaming\python\python36\site-packages (from pefile>=2017.8.1->pyinstaller) (0.17.1) C:\Users\Ankit.Aggarwal>pyinstaller
'pyinstaller' is not recognized as an internal or external command, operable program or batch file.
However , getting above error on executing simple pyinstaller command. What am I missing?