You just have to use the "Update" method on myDa dataadapter. First you must create the update commands, the easiest way is to use "OledbCommandBuilder".
Code:
Dim query As String = "Select Nome,Taxa,Valor,Data from view1 where Month(Data) = Month('" & a & "') and Nome ='" & ComboBox2.Text & "'"
Dim cmd As New OleDbCommand(query, con)
Dim myDA As OleDbDataAdapter = New OleDbDataAdapter(cmd)
con.Open()
Dim cmdbld As New OleDbCommandBuilder  ' Add this line
cmdbld.DataAdapter = myDa                       'add this line
myDA.Fill(myDataSet, "Data")   
View1DataGridView.DataSource = myDataSet.Tables("Data")  ' No need to use Default view
'con.Close()  ' Don't close the connection

    Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        myDa.Update(dt)
    End Sub