To use a VPN on iOS:

It seems like you might be referring to using a VPN on iOS to access content or websites like知乎. However, iOS does not come with built-in VPN services, but you can use third-party VPN apps on iOS to block or block access to specific websites.

1. Download a VPN app from the App Store.
2. Install the VPN app.
3. Configure the VPN settings according to your needs.
4. Use the VPN to block or block access to specific websites or sites like知乎.

Note: While this can help you access the internet, using a VPN on the internet for specific content sites like知乎 is not advisable and could be considered unethical or illegal. Always use VPNs responsibly and ethically.