Okay download the Navi_X.zip file.
Then use a program such as iExplorer and on the left side of the program select "Root".
From there, you should now be in the root of your iPhone. Select User>Downloads. Place the Navi_X.zip file (you downloaded on your computer) in the downloads folder of the root of your phone.
Now, upon completing that go to your phone and boot up XBMC.
First, go to settings and make sure the Confluence theme is picked. Back out of there and while still in the settings menu, select Add-ons.
Select Install from zip file. Click Home Folder and navigate to the Downloads folder. Select the Navi_X.zip file. It should now be on XBMC.
Back out of there all the way to the main horizontal menu and select Programs.
There you should see Navi-X installed and be able to select it and fire it up.
Hope that helps.