Hi Hossain,
Solution is quite simple for your issue.
You need to download the template for Customers (from BC), once you download the template click on 4th tab "Contacts".
Give Account Id, Contact Id's & Mark Contact Permission as "X" if you want to enable the permissions if not then keep it blank. Don't provide any other data.
Go to the Migration tool upload the file and upload it (slect the option of update the existing accounts).
Above steps will resolve your issue.
Regards,
K.F.