LongoMatch already has Sync2desk plugin added in the software. You do not have to install Sync2Desk, you only have to activate the license.
Access to "My products" to find the link to activate Sync2Desk's license.
Note that you will be redirected to a JAVA based web. So, if JAVA is not enabled, you will see a JAVA error in your screen
Once the license is active, you will see the expiration time and the link to activate the license will disappear as you can only activate the license in one computer.
Now that the license is active in your computer, if you access to LongoMatch and click on "Import" option, you will see a pop-up window that allows you to choose "Import Tag2Win projects".