To do this:-
First, click on any WPForms form to edit it …
… then click on the settings tab to open the form settings.
Next, click on the Noptin panel to open the Noptin settings.
Finally, enable Noptin subscriptions…
… then map the fields on your WPForms form to Noptin fields.
Remember to save your changes.
From now on, whenever someone fills your WPForms form…
… they will be added to your Noptin subscribers’ list.