You can set these notification in the creation of a form or by revising an existing Form in multiple choice questions.
Select Forms on the side tool bar
To change an existing choose the Form that you need to get Answers Notifications from.
Click the Revisions tab
Select the Latest Revision to Edit
Create a New Revision of the Form
This will create a Draft of the form where you can Click into and edit.
Add tags to Notify People Tagged With
Save
When creating notifications while A new Form, you add the tags while creating the element.
See the How to Create Forms help article if any questions on how to create forms.