Here is your code for part 2 of my comments adjusted to do the job of importing a single file, all you need to do is write the sub that collects the file names and call the sub below for each file in turn;
Public Sub ImportExcelFielToTable(ExcelFile As String, TargetTable As String)
Dim koneksi_excel As New System.Data.OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source='" & ExcelFile & "';Extended Properties=""Excel 12.0 Xml;HDR=YES""")
koneksi_excel.Open()
Dim query_excel As String = "Select * from [Sheet1$]"
Dim cmd As OleDbCommand = New OleDbCommand(query_excel, koneksi_excel)
Dim rd As OleDbDataReader
rd = cmd.ExecuteReader()
Using koneksi As New SqlConnection("server=DESKTOP-KJQ8PNO\SQLEXPRESS;DATABASE=otto;Integrated Security=True")
koneksi.Open()
Using bulkcopy As SqlBulkCopy = New SqlBulkCopy(koneksi)
bulkcopy.DestinationTableName = TargetTable
bulkcopy.BulkCopyTimeout = 600
bulkcopy.WriteToServer(rd)
rd.Close()
MsgBox("Data uploaded to database", MsgBoxStyle.Information, "Uploaded")
TextBox1.Text = ""
End Using
koneksi.Close()
End Using
End Sub