FIIL a var with free room period

[sal21]

I have this listview with a number of room.

the first column contain a KEY and ROOM type.

now i need to store in a combobox FREE CAMERA the not reserved period, for each room, example:

10-SINGOLA - 09/02/2021-20/02/2021
11-SINGOLA - 09/02/2021-20/02/2021
11-SINGOLA - 28/02/2021-28/02/2021
13-SINGOLA - 01/02/2021-20/02/2021
13-SINGOLA - 27/02/2021-28/02/2021
...
16-SINGOLA - 01/02/2021-28/02/2021
17-SINGOLA - 01/02/2021-28/02/2021
18-SINGOLA - 01/02/2021-28/02/2021
19-SINGOLA - 01/02/2021-28/02/2021

Note:
The header contain the number of days
R room is reserved
i just have a variable ANNO=2021
i just have a variable MESE=2 (Febrary)