Option Explicit
Sub Convert_Formula_To_VBA()
    Dim ws As Worksheet
        Set ws = ThisWorkbook.Worksheets("Sheet1")
        With ws
    With .Range("D4")
     .Formula = "=COUNTIFS($A$1:$A$20,"">=01/01/2020"",$A$1:$A$20,""<=10/01/2020"")"
                .Value = .Value
            End With
        End With
End Sub