vba excel insert quantity from textbox, search for the product and if there is a match sum the quantities or just add a new row

I would really appreciate any help.

Here is the issue: I want to input details to stock an item. By textbook the user inputs quantity and date and by combobox selects the item. I want the sub to search for this item in stock. If there is stock then to sum the quantites and update the date. Otherwise to add a new row at the stock sheet.

Any help is desirable! thank you in advance

    Private Sub CommandButton1_Click()
    Dim x As Integer
    Dim nextrow As Range
    Dim i As Integer

    On Error GoTo cmdStock_Click_Error

    Set nextrow = Sheet8.Cells(Rows.Count, 6).End(xlUp).Offset(1, 0)
    For x = 1 To 4
    If Me.Controls("Stock" & x).Value = "" Then
    MsgBox "Missing data"
    Exit Sub
    End If
    Next

    For i = 1 To 10
    If WorksheetFunction.CountIf(Sheet8.Range("D:D"), Me.Stock2.Value) > 0 Then
      Cells("E,i").Value = Cells("E,i") + Me.Stock3.Value
      Cells("F,i").Value = Me.Stock3.Value
      MsgBox "Stock is now updated"
    Exit Sub
    End If
    Next i

    For x = 1 To 4
    nextrow = Me.Controls("Stock" & x).Value
    Set nextrow = nextrow.Offset(0, 1)
    Next
   'clear
    For x = 1 To 4
    Me.Controls("Stock" & x).Value = ""
    Next

    On Error GoTo 0
    Exit Sub
    cmdStock_Click_Error:
    MsgBox "Error " & Err.number & " (" & Err.Description & ") in procedure cmdStock_Click of Form frmStock"
    End Sub