Umberto,
The path in the Addon file for the Exclude files is incorrect. It includes the word scenery which is not required. Checking the paths for all the FSDT airports I own does not include the scenery folder. That is assumed.
I edited it and removed '\scenery'. When P3D started it rebuilt its scenery indexes. That had not previously happened.
I managed to create my first custom jetway after following the video tutorial. The only thing that foxed me was finding and running the Control Panel.