Access to server inside Lan behind the MikroTik

RouterOS Beginner Basics
1

Hi. I have a problem.

My client has a server inside a LAN. I created a tunnel to connect to another server connected to MikroTik and everything works fine.

Now they have another server connected to a TP-Link router, but the client wants to connect to this server over VPN.

MikroTik ping the server, but when I connect over VPN with certificate the computer can not ping.
NOTE: I can not move this server to MikroTik because it has years of documentation and an application and can not be lost.

Thank for your attention.

2

Provide a diagram at least of the networking involved.

3

I would love to see a more detailed description with a diagram. I have something similar to this that needs to be addressed.