I finally found the solution to manage to reinstall the ATR.
Following the indication of last Thursday proposing an update I had uninstalled the ATR to download it again, and that makes me a failure of download, so here is how I proceeded:
1/relaunch the simulator and go to the content manager
2/ type ATR in the search bar
3/ click on the 3 dots to expand the content
4/ select ATR COMMON and download it
5/ then select the liveries and download them
and There you go