- restart your computer and hold down the Command+R (⌘+R) keys simultaneously when you hear the boot chime
- open a Terminal window from the Utilities drop-down menu at the top of the screen
- Type the following into the Terminal window: csrutil disable
- restart for changes to take effect.
restart in macOS Recovery mode again with the Command+R (⌘+R) keys, then open a Terminal window and type: csrutil enable