This is the only way to use an open VPN on ChromeOS.
Click on your profile picture in the bottom left corner.
Click on settings.
Click on add connection.
Click on OpenVPN / L2TP
Fill this out depending on the VPN your using:
Done.
Click on your profile picture in the bottom left corner.
Click on settings.
Click on add connection.
Click on OpenVPN / L2TP
Fill this out depending on the VPN your using:

Done.