You can redirect users to a page of your choice with the message you like , just by entering the URL in the formlets settings under "submission success page"
if you would not find the field , you need to scroll down the settings pane with more options
always add http:// or https:// in front of the url
From the Formlet Builder, select the Formlet tab
Scroll to the Submission Success Page section
Toggle ON the Redirect to Web Page switch selecter
Enter desired Web Page URL
When the user completes the Formlet and Submits, they will be directed to the Web Page URL you have listed in the steps above.