Translation:-
"A special key is needed to unscrew the wheels. Unfortunately, I don't have any. What exactly is it for a key and how could I come?"
A photo may help, but if it is only on one nut/bolt on each wheel it may be an anti theft device of which there are many and not all genuine Fiat.
If it is that have you looked in the glove pocket or spare wheel area for something like this below.
Note if so , be careful undoing or tightening and do not use an impact/air gun to do it as the break easily!
Finally if it is that sort of device and you cannot find the key then often tyre depots have a tool to remove it, but then you will need to buy new nuts to replace them.