Accepting more than one appointment per time slot with Appointments+

I am trying to accept more than one appointment per time slot. This isn’t possible even with capacity set to 10.

The FAQ says to:

“Capacity field is for limiting the workforce, not for increasing it. You have two alternatives to achieve this: a) Use dummy service providers b) Add these codes in functions.php and modify as required:

function increase_capacity( $capacity, $service_id, $worker_id ) {

return 10;

}

add_filter( ‘app_get_capacity’, ‘increase_capacity’, 10, 3 );”

How do I add these codes to the functions.php?

Thanks.