Public Class Form1
    Dim dataTable As DataTable
    Dim dataSet As DataSet = New DataSet
    'Dim da As System.Data.Common.DataAdapter = New System.Data.Common.DataAdapter 


    Dim i As Integer
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        dataSet.ReadXml("D:\xml\333\ORDERS_5bcd067b-fbd5-4a4c-9785-5feffddfb3c6.xml")
        i = 0
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        DataGridView1.DataSource = dataSet.Tables(i)
        If i < dataSet.Tables.Count - 1 Then
            i = i + 1
        Else
            i = 0
        End If
    End Sub

End Class

//Взять первую таблицу из DataSet и подключить в качестве источника данных в DataGridView
DataGridView_main.DataSource = DataSet_main.Tables[0]

Dim i As Integer 
на 
Private i As Integer