To import the client's data, you need to have the permission to do that. If you also have a permission to import settings, you can specify the fields required in clients data import (the same way you do that for candidates data import).
First, you need to prepare the CSV file according to these guidelines.
To start the process, open the data import option in the system.
Then, click on Clients:
You can perform the clients data import exactly the same way you do it for the candidates - the full description is available here.
The uploaded CSV file is being verified before the import.
When the import starts, you will be informed about it's status.
You can stop the import process anytime and get back to it later, because the full history of imports is available to you all the time (both the performed ones and the ones that were started but didn't end).
If the data from the CSV are supposed to be merged with the existing ones, their names should be identical with the names of the Clients in the system (size of the letters is essential).