How do I roll back to Windows 10 after installing Windows 7? :/

I had Windows 10 installed, then I went ahead and installed Windows 7 without formatting the drive or deleting anything. Now I’m sitting here with Windows 7, but I've changed my mind. 😵 I want to get rid of this version and go back to Windows 10.

Is there a way to do this without doing a full reinstall of Windows 10, since I didn't wipe the disk? How do I tell the computer to boot from Windows 10 instead of Windows 7? Is that even possible?

Just click on the Start button, type System Configuration into the Run box, and then head over to the Boot tab—from there, you can set Windows 10 as your default OS.

Nope 😢. He can't even see Windows 10 on my end. System Configuration only shows Windows 7. Windows 7 is the main OS now, and he clearly hasn't realized Windows 10 exists yet. Even though they were born after Windows 7 😉 .