Microsoft Access 掲示板

下記の関数を作成して、

Public Sub CtlVCenter2(ReportName As String, ControlName As String, ControlName1 As String, ControlName2 As String)
    DoCmd.OpenReport ReportName, acViewDesign
    
    Dim R As Access.Report
    Set R = Reports(ReportName)
    
    Dim C As Access.Control
    Set C = R.Controls(ControlName)
    Dim C1 As Access.Control
    Set C1 = R.Controls(ControlName1)
    Dim C2 As Access.Control
    Set C2 = R.Controls(ControlName2)
    
    C.Top = (C1.Top + C2.Top) / 2
End Sub

イミディエイトで下記を実行。

Call CtlVCenter2("レポート名", "フィールド3", "フィールド1", "フィールド2")

以上でどうでしょうか。