Override DNS Settings in Swift programmatically

I have used IPSec VPN to use another DNS it works fine but the problem is that it uses my server internet bandwidth. What I want is that internet of users must be used not my server bandwidth.

The purpose of my goal is that is there any way to override DNS Settings of iOS in swift or use another DNS programmatically ? Please help me. I have been trying from 01 week I failed to achieve it.

Thanks in advance.