You can easily create a new survey for an existing client from the Client & Form Settings page.

To reach it, get started on the main Admin Page.

Select a client, head to the Clients tab and use the Client & Form Settings link, or simply use the Quick Jump bar.

The top of the Client Administration page has a Survey section. 

Look for a Create New Survey for Client_Name button below all the listed surveys.

A Survey Administration page will open, and the only required field to create a new survey is the Survey Name.

Scroll to the bottom of the page and use the Add New button.