how do I clean boot a wundows phone running 8.1

[out of thebox]

Working with start up configurations in an mobile operating system environment

 

[das_stig]

If you mean full wipe back to factory fresh settings for Lumia, with the device powered off.

Hold volume down and insert power cable until you see exclamation mark comes up on the screen.

Enter this button combination, Volume Up, Volume Down, Power, Volume Down.

Phone will reboot and reinstall fresh version foe WP81, may take a few minutes.