Question: how to transfer iphone backup to external hard drive windows 10?
Answer: Close iTunes if the program is open on your computer.
Connect the external USB hard drive you want to use to store videos from the iPhone to the computer. ... 
Press "Windows-E" to open File Explorer. ... 
Connect the data sync cable to the iPhone and a second USB port on the computer. ... 
Press "Window-R" to open a Run box.