This will disconnect you from your Citrix desktop session, but when you log back in to the Citrix desktop the system will remember your dual screen preference and will properly detect which monitors to use as your primary and secondary screens (it detects this setting from your local computer). This will expand the Citrix desktop across both monitors. (To do this you can click at the top of the Citrix session and drag the window so that it is showing up halfway on each of your monitors.) Drag the Citrix desktop session window so that it spans across both of your screens.
From inside the Citrix desktop, if you are already in a full-screen view, click on the black connection bar then click on Window to go into a windowed view.Here are the steps to expand your session to use more than one monitor. When you login to the Citrix desktop, it may default to only using a single monitor.