Power wash refers to a factory reset, so clean slate. It does allow a re-install of Chrome OS onto the Chromebook.
Push Escape + Refresh + Power on the keyboard
Push Control + D on the Keyboard
Follow the prompts on the screen and your device will be reset.
Other pictoral guide at https://www.howtogeek.com/210817/how-to-enable-developer-mode-on-your-chromebook/
Note: If for some reason the device has been provisioned by a business or school, you will need to talk to the Device administrator to clear this from Google Device management (MDM).