You can easily add more participants to a group booking which is already in your calendar.
Click on the booking in your bookings screen and click on the Customers tab. Here you can view and edit any customer on the booking.
If there are spaces free, click Add customer to add more customers to the booking:
Select an existing customer or create a new customer
The customer has been added as a participant of the booking. You can now edit the number of spaces they'll be taking, update their pricing or status, send a payment request, or add any notes to that customer.
You can also increase the occupancy of an existing booking. This guide will take you through it.