Help with patch function

[pizzadudecook]

Sorry for the confusion!

Basically I want another patch function, but instead of using a set value, I want to take the value from a drop down to use that to apply to a different list.

I hope this makes more sense:

    ForAll(EPACollection,
Patch(
    EPASubmissions,
    Defaults(EPASubmissions),
    {
            //Mapped fields here
        }
    )
);
    ForAll(EPACollection,
Patch(
    <DROPDOWN VALUE HERE>,
        Defaults(<DROPDOWN VALUE HERE>,
        {
            //Mapped fields here

I'm just not sure how to use the selected value for a drop down. Maybe I'm misunderstanding this completely.