Go to "Team>Schedule".
From the calendar, select the event you wish to add a form to. You can either select a pre-existing event or create a new visit to add the form to by going to "+ New Event" and "Visit to Customer".
Once you are on the visit page, scroll down to the "Visit Forms" section.
Under the Visit Forms section, you will see checkboxes with your previously created forms. Select the form you wish to attach to your visit.
When you are done either creating or editing your visit and attaching the form, scroll down to the bottom of the page. There you will see an "Update Visit" button if you edited an existing visit or a "Create Visit" button if it's a new visit.