Hi MadurangaSirisena,
I am Dave, I will help you with this.
1
mm/dd/yyyy should be the default date format in File Explorer, please provide a screenshot of your file Explorer window, showing the columns and date format.
2
Open the Settings app, then go to Time and Language - Language and Region
Click 'Administrative Language Settings
On the resulting dialog, select the formats tab and then click 'Additional Settings'
Please provide a screenshot of the Date tab on the next dialog.