Looking for a single text value and returning 1 or multiple text values in one cell

Try this

    With Worksheets("WinnersList")
        a = .Range("a2", .Cells(Rows.Count, 1).End(xlUp))
    End With
    For i = 1 To UBound(a)
        If .exists(a(i, 1)) Then a(i, 1) = .Item(a(i, 1))
    Next
    With Worksheets("WinnersList")
        .Range("m2").Resize(UBound(a)) = a
    End With