Modules & VBA :: Data Append From Excel With Condition?

I am trying to append some data from an excel sheet. Following code used for same and successful. However, i need to put few condition while importing the data to the Access table. i.e;

Table : tblMain
Filed : Vessel, Voyage, contianerNo, ......, ......, .....,

while importing, need to check whrt "containerNo" which is importing already in the table under the particular voyage. If yes error msg should pop up warning that the particular container is already exists. If same container number is already exists in the same table under a different voyage, data should be imported without any error.

Code

Private Sub Command0_Click()
Dim Filepath As String
Filepath = "D:Xxxx bl_Impts_main.xlsx"
If FileExist(Filepath) Then
DoCmd.TransferSpreadsheet acImport, , "MainImportsfromxls", Filepath, True

[Code] .....

Code Source : [URL]