How to backup windows 10 system image

First you need a USB external drive connected
Right click start menu > (type in search bar:Control panel)Control Panel > File History (if your view is small/large icons) > System Image Backup (bottom left corner of window)

to restore:
left click start menu > Settings > Update & security > Recovery > Advanced Startup > Restart Now > When your PC restarts, go to Troubleshoot, Advanced Options, and then choose System image recovery.