非常感谢@dr.null的指导
表格中的代码1

Public Class Form1
    Dim itrservice As New ItemtransfersService()
    Private Invno As String
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        DataGridView1.DataSource = itrservice.GetLoadItemTransfersMaster()
        DataGridView1.ReadOnly = True
    End Sub
    Private Sub DataGridView1_CellContentClick(sender As Object, e As DataGridViewCellEventArgs) Handles DataGridView1.CellContentClick
        If e.ColumnIndex = 0 Then
            If DataGridView1.SelectedRows.Count > 0 Then ' make sure user select at least 1 row
                Dim Invno As String = DataGridView1.SelectedRows(0).Cells(0).Value.tostring & String.Empty
 Dim item = DirectCast(DataGridView1.SelectedRows(0).DataBoundItem, ItemTransfers)
                Using frm = New Form2(item)
                    If frm.ShowDialog() = DialogResult.OK Then
                    End If
                End Using
            End If
        End If
    End Sub
End Class
Public Class ItemtransfersService
    Public Function GetOledbConnectionString() As String
        Return "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\dapperdemo.accdb;Persist Security Info=False;"
    End Function
    Private ReadOnly _conn As OleDbConnection
    Private _connectionString As String = GetOledbConnectionString()
    Public Sub New()
        _conn = New OleDbConnection(_connectionString)
    End Sub
    Public Function GetLoadItemTransfersMaster() As IEnumerable(Of ItemTransfers)
        Dim sql = "SELECT * FROM ItemTransfers"
        Using _conn = New OleDbConnection(GetOledbConnectionString())
            Return _conn.Query(Of ItemTransfers)(sql).ToList()
        End Using
    End Function
    Public Function GetItemTransfersDetail(ByVal Invno As String) As IEnumerable(Of ItemTransfersDetail)
        Dim sql = $"SELECT * FROM ItemTransfersDetail WHERE Invno = '{Invno}'"
        Using _conn = New OleDbConnection(GetOledbConnectionString())
            Return _conn.Query(Of ItemTransfersDetail)(sql).ToList()
        End Using
    End Function
    Public Function GetItemTransfersMaster(ByVal Invno As String) As IEnumerable(Of ItemTransfers)
        Dim sql = $"SELECT * FROM ItemTransfers WHERE Invno = '{Invno}'"
        Using _conn = New OleDbConnection(GetOledbConnectionString())
            Return _conn.Query(Of ItemTransfers)(sql).ToList()
        End Using
    End Function
End Class
Public Class ItemTransfers
    Public Property Invno() As String
    Public Property HeaderInvno() As Integer
    Public Property CreatedBy() As String
    Public Property Created() As DateTime
    Public Property ModifiedBy() As String
    Public Property Modified() As DateTime
    Public Property ItemTransfersDetail() As New List(Of ItemTransfersDetail)()
End Class
Public Class ItemTransfersDetail
    Public Property Id() As Integer
    Public Property No() As Integer
    Public Property Invno() As String
    Public Property CodeProduct() As String
    Public Property Barcode() As String
    Public Property Colorcode() As String
    Public Property Size() As String
    Public Property Qty() As Integer
End Class

表单中的代码2

Public Class Form2
    Inherits Form
Dim itrservice As New ItemtransfersService()
    Sub New()
        InitializeComponent()
    End Sub
 Public Sub New(item As ItemTransfers)
        Me.New
        DataGridView1.DataSource = itrservice.GetItemTransfersDetail(Invno)
        DataGridView1.Columns(0).Visible = False
        TextBox1.Text = item.Invno
        TextBox2.Text = item.Created
 End Sub
End Class