How to add a second VPN on the same network

Hello experts,

Im new to fortigate and IT in general, and i have a question. In my company there is an existing VPN to the network connected to an external client.

Now i want to connect with another client via VPN but the problem is that i want him to see only a specific server that is on a different internal network. e.g (172.16.10 the main network, 172.16.11 the other network) and i dont want him to use the DNS that the other client uses. 

How do i do that?

Thanks in advance and sorry for the newb questions