To turn on the COVID-19 Form, go to Setup > Form Settings. You can customize the form by going to the COVID-19 tab.
Once the form is on, it will be sent as part of your appointment reminder (note: the reminder email, not the confirmation email - this way the form is being completed closer to the actual appointment). The client will click a button, and the form will open in their web browser. They'll sign and submit the form. Once they have done that their appointment will be marked with a checkmark so you know they have been prescreened.
What to do if there's no checkmark?
At the end of each day, look at tomorrow's appointments. For any appointment that does not have a checkmark, contact the client and ask them to complete the form, or you can do it verbally over the phone.
If done verbally, you can open the appointment and you'll see a checkbox for "Covid-19 Pre-screening". Simply check the box and save the appointment and the checkmark will appear to show that prescreening is complete.
If the client completed the form online, you'll see "(view)" next to the form, so you can open and view the form they signed.