How to correctly redirect a request via RDP from the gateway to a specific computer?

Question

Computer networks

Good day. Please tell me how (and how) it is correct and with minimal troubles to redirect an RDP request from the gateway to a specific computer. The point is: Previously, the server had its own external IP address and was connected directly to it via RDP. Now the server is moving to another network, and there it becomes a LAN, but it is necessary to maintain the ability to connect to the server via the Internet. Network diagram: the Internet comes to the gateway (a regular PC with win7 on board), then a router, then there will be a server. How (or what programs/settings) can be achieved so that when connecting remotely to the external IP address of the gateway, there is a correct redirect to the destination server? Please do not offer various third-party programs, because. there is no way to install them on all client machines.