Warning: if you follow this guide, you won't be able to use certain features of macOS anymore (iOS apps, Apple Pay, ...)
- Reboot your Mac into recovery mode
- shutdown macOS
- after macOS has shut down, hold down the power button until it says something about "options"
- choose options and not your harddrive
- you will be asked to log in, do so
- start Terminal from the top menu
Type these two commands: