Hi.
According to your description, you want to fall back to Win7.
What is your current PC version? Win10?
If the Win10 installation has not been more than a month old, you can directly fall back to Win7. The steps are as follows:
First you need to back up your important files and more;
Settings> Update and Security> click "Restore" on the left, the button to fall back to Win7 will be displayed on the right side, click "Start", select the reason for the rollback, and then confirm the fallback to Win7.
If Win10 is installed for more than a month, you can only reinstall Win7 using a USB flash drive as a boot disk.
Hope the information is helpful.
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