Ok, I grabbed a few screen shots for you as well. Here is a site that will link you to MEBx setup that enables AMT: http://h10032.www1.hp.com/ctg/Manual/c03883429
When power on your ProDesk G3, you can access the MEBx setup by pressing Ctrl+P or they also say F6 or Escape will get you there. Intel AMT runs on a different IP address than what your OS gets. You can assign DHCP or a static IP address and setup your admin password. You can then access the portal from http://ipaddress:16992 There should be a method of access what would show on the screen through a KVM like access but I use MeshCentral for that so I couldn't tell you how to do it without.
Hopefully, that gives you a start. Feel free to reach back out if you have any questions. Thank you!
Glad I could help! 😃