Backing up your videos and other files to an external drive and accessing them after a factory reset is possible.
Plug in your external drive (USB flash drive or external hard drive) to your computer. Navigate to the folders where your videos and other files are located. Select the files and copy them.
Go to your external drive in File Explorer. Right-click in the external drive's window and choose "Paste" to copy your files to the external drive.
Remove the ext. drive.
================================
Once the factory reset is complete, you'll have a fresh installation of Windows.
Plug in your external drive again.
In File Explorer, navigate to your external drive, and you should see the files you backed up earlier. You can now copy them back to your computer or access them directly from the external drive.