You'll notice that pgAdmin 3 has been deprecated and replaced with pgAdmin 4, starting with Spire 3.2.  In some instances your PC may already have a valid server entry from a prior compatible installation, but most likely you'll have to create a new one.  

Note:  For extra help, please refer to this: 

These are the steps to add a server entry on the server PC:

  1. Look for pgAdmin 4 in your Start menu and run it:

  2. This should start the pgAdmin application in a browser.  Right-click on "Servers" and select "Register" then "Server...":

  3. Give the server an ad-hoc friendly name:

  4. Go to the "Connection" tab and enter localhost in the "Host" field.  Enter the database master password in the "Password" field and click "Save":

  5. You should now be able to expand your server entry just like with prior versions of pgAdmin: