Salesforce Integration: How to update existing leads?

Hello, I have a client looking to put a survey out to his existing clients. Was seeing if this is something that will sync to the current contact in the CRM or it only creates new contacts in the leads section? Thanks.

You can also update the existing leads with the new data. Once you complete the integration select "Update Existing Entry" from the Duplicate Check dropdown.

Here is the guide: How-to-Setup-Salesforce-Integration