Ford uses the APIM interrogator utility. Run this to obtain the xml file you need to upload to Ford.
However, If you upgraded your Sync APIM from Sync 3.0, it will not matter, you will not get 3.4 updates since the APIM was never meant to have it. Also, true for many 3.2+ APIMs that are not eligible for the 3.4 update. Just because you put 3.4 on your APIM does not mean you will get updates for it. Most likely, you will continue to get the updates for the original Sync version.
To report the update, go to your Ford Owner site for your region, sign in and go to the Sync update section.