Will it be possible to auto link the Contact/Account to Lead uploaded through Data import option. The unique ID of Contact /Account ID shall be used in bulk upload file for linking the contact/account.
Unfortunately, are no such basic tools for imported records/
The only way to achieve your business task is to create a new business process with a start signal with an event that should trigger the signal (Record added / Record modified).
Please note you should enable this business process before the import and disable it after.
