Need help to create windows 7 installation media for os reinstall

You can create a bootable Windows 7 installation USB drive by using the Windows 7 ISO and the Windows USB/DVD Download Tool, which is a free utility provided by Microsoft. 

What you'll need:
    A USB flash drive with at least 4GB of free space (note: all data on the drive will be erased).
    A valid Windows 7 ISO file (downloaded legally).
    Your Windows 7 product key.

How to Create Windows 7 Installation Media:

1. Download the Windows 7 ISO file
2. Download the Windows USB/DVD Download Tool
3. Launch the Windows USB/DVD Download Tool.
4. Create the bootable USB
5. Boot from the USB and install Windows 7
    - Insert the USB into your target PC.
    - Restart the PC and access the BIOS/UEFI settings (usually by pressing F2, F12, Del, or Esc during startup).
    - Set the USB drive as the primary boot device.
    - Save changes and restart.
    - Follow the on-screen instructions to perform a clean installation using your product key.