To factory reset an ASUS CB3-451 Chromebook, you'll need to use the "Powerwash" feature. First, sign out of your Chromebook, then press and hold Ctrl + Alt + Shift + r. Select "Restart", and then choose "Powerwash" and "Continue" when prompted. Follow the on-screen instructions to sign in with your Google Account after the reset is complete. 

Here's a more detailed breakdown:

1. Sign out: Sign out of your Chromebook's user account. 

    

2. Press key combination: Press and hold Ctrl + Alt + Shift + r simultaneously. 

    

3. Select Restart: In the pop-up menu, select "Restart". 

    

4. Choose Powerwash: In the subsequent window, select "Powerwash" and then "Continue". 

    

5. Sign in: After the reset, your Chromebook will restart and display the initial setup screen. Follow the instructions to sign in with your Google Account, which will be the owner account after the reset.