This might help https://www.bestvpn.com/best-chromebook-vpn/ Also try Googling 'Chrome OS VPN' for more options.
The link suggests VPNs that are Chrome OS friendly where they supply a Chrome extension that you would use to connect to the VPN.
Other VPN companies you can create connections manually to but usually it's using out of date protocols so you're not as secure as you would be using a VPN company's app or Chrome extension as in this instance.
Hope that helps.
