Choose a Mac
You can use the Server app on the computer that will be your server, or you can use it to remotely manage a computer with macOS Server.
When you’re presented with the “Choose a Mac” dialog, if you choose the option for “This Mac,” the Server app will promote your Mac to be a server. Other Mac computers on your local network with macOS Server enabled appear in this dialog. You can also add other servers by their IP address or hostname.
You can manage remote Mac computers with macOS Server installed only if the “Allow remote administration using Server” option is checked on the remote computer. This option is in the Settings pane of the Server app. You need to enable this locally on the remote server before managing it from another Mac.
If you don’t see the server you expect, check your network connection or the network connection of the other server.