Clients are registered through the Web or App. This record is recorded in:

Website & Networks → Management of external users Registered Users

This will be the list of all users who have registered. In which you can change the password through the edit button, You can also send by email the password you had, through the yellow envelope icon.

And even, you can also unsubscribe the user and delete permanently.

You can also do it from the client's tab. 

Click here to see more details.