CHANGE format DATA (examples "1-1-2018" to "January")

[DaGi07]

Hello,
I’d like convert the value of column type Data [Periodo] from “1-1-2018” to “January” (only month)
I tried with TEXT([Periodo]),“mmmm”) but it doesn’t work.

I tried also creating a new virtual column called “Month” with the following app formula but it doesn’t work when i group data in tables view
SWITCH(MONTH([Periodo]),
1,“Gennaio”,
2,“Febbraio”,
3,“Marzo”,
4,“Aprile”,
5,“Maggio”,
6,“Giugno”,
7,“Luglio”,
8,“Agosto”,
9,“Settembre”,
10,“Ottobre”,
11,“Novembre”,
12,“Dicembre”,
“”)

How can i change the format data correctly?
TKS