Create Bootable USB for Windows

My friend's PC needs to be downgraded to Windows 7 from Windows 10. Unfortunately the computer crashed while downgrading but requires a Windows 7 disc to continue. We don't have that here with us. We borrowed a friend's Windows 7 Ultimate on a USB - its not the .ISO file but it has lots of files. Is there an easy way to create a bootable USB from the flash drive for Windows?

Many thanks,

Dan