sorting lists

[Exsto]

Hello,
I would like a default sorting of my lists for changing the date (Lead, Contacts, etc.). I found it on: custom /Expo/Custom/Resources/layout/

        
        "name": "modifiedAt",
        "notSortable": true,
        "align": "left"
    }

What should I add to order it in ascending / descending order?
thanks

[Exsto]

Please could someone give me some suggestions.
Thanks so much