Save any important files first, because enabling Developer Mode can erase local data
Turn off the Chromebook
Press and hold Esc + Refresh, then press Power
When the recovery screen appears, press Ctrl + D
Press Enter to confirm turning off OS verification
Wait for the Chromebook to restart and enable Developer Mode
Follow the on-screen setup prompts
To exit Developer Mode, turn off the Chromebook, then press Space at the recovery screen and confirm