When you need to assign clients to your sales people, you should do it from the web version

Clients > Clients - user

On the following screen click on the user to assign the client. Clients may have only on user assign. click on the save button once you have done the changes and sync the devices.

On the users box you may select the user that you need to see the clients assigned

you may know the users number at SelBuk.com > Login > Account managment > user/password > User 6 Devices Configuration >>> Users Chart second column on the left