Hi,
Go to menu Components -> Visforms in the administration panel of your website.
If you are on Joomla! 3.7.1 you should have installed Visforms 3.8.24, therefore you see the Visforms Dashboard then.
Click the "Forms" Panel or Click "Forms" in the sidebar menu there
You see a list of all forms, which you have created, then
Check the box in front of the form item, which you want to edit, then click the "Edit" Button
This will lead you to the "edit form view" as mentioned in the documentation.
You should see at least 7 tabs there: Basic, Result, Mail Options, Spam Protection, Advanced, Dataview in Frontend, Form Permission.
The 3rd tab from the left is the one you are looking for.
If you do not see any tabs, please check out the Visforms FAQ's
vi-solutions.de/en/documentations/visforms/faqs-visforms
There is a FAQ "Tabs are missing in the form configuration screen" (3rd from the bottom).
Regards,
Aicha