When users click on "Open Database View" in the web app for Rairser's Edge they will download an ICA file. You will need to have Citrix Workspace installed in order to open the file. You can download the app from here: Download Citrix Workspace App for Windows, Mac and Chrome - Citrix
Most of the time Citrix should automatically set itself as the default app for ICA files. In some cases, you will have to do so yourself. Normally the app is located under "C:/Program Files (x86)/Citrix", choose the app "CDViewer".