Create Custom Function: Update Appt date & time field

Create Custom Function: Update Appt date & time field

I created a custom field for Appointment date and time. 

I want to create a custom function that allows my lead record to be updated with the appointment date and time booked through Zoho bookings. 

For ex: Sally Sue books a consultation for a Marketing Strategy for 09/10/2024 through my Zoho bookings site. 

How can I get the appointment date automatically added to my lead record?