With the "Confirmation Page" field in the Web Forms "Settings" tab enables you to redirect users to a custom Web Page or Landing Page after they have submitted the form. Here are the steps to create a basic Page and link a Web Form to it.
• Create a new Web Page or Landing Page called "Thank You". (See How to create a Web Page)
• Navigate to Content > Web Forms.
• Locate the Web Form you would like to add a redirect to and click the Form Name hyperlink or edit pencil icon under the "Actions" column.
• Under the "Settings" tab select the newly created "Thank You" page from the "Confirmation Page" drop down selector.
• Click Save.