1. Go to Forms > Forms and Submissions and click the form you want to modify.
2. Click the green Manage Form button.
3. Click to expand Form Settings in the lower left.
4. Scroll down to Email Notifications.
5. Click the New Notification button to create a new notification (or click Edit under an existing notification).
6. Scroll down to where it says "From" Email Address Type and choose Custom Email.
7. Type in the appropriate address in the Custom "From" Email Address field.
8. Click the Save Form button.
9. You should be all set!