I'm not sure exactly what you are asking, but I'll give it a try.
If you want to pass the scoped variable named selectedDate to an EL function that you've defined in your TLD (let's say that the function is named whatever), you'd just list in the parameter list. Such as:
But I'm not sure that's what you are asking.
Also, what is the sense of dropping the 'o' in the name formateDropDwnDate? Improve clarity by avoiding unnecessary abbreviations: name it formatDropDownDate using complete and real words (note that there's no 'e' in format).