How can I get my second monitor to match the resolution of my 5K iMac?

Chuck has a 5K iMac and a second LG 5K monitor. But he can't get the resolution to match. The window ends up 50% smaller. Leo says Apple has taken a lot of control away from users. He suggests trying an app called SwitchResX. It'll let you choose any resolution and frame rate your monitor will support.