remove the link "Manage My Bookings"

<?php

add_action( 'wp_head', 'remove_my_action' );
function remove_my_action() {
	remove_action('em_booking_form_status_already_booked', 'em_booking_form_status_already_booked');
}
function em_booking_form_status_already_booked_custom(){
	echo get_option('dbem_bookings_form_msg_attending');
}
add_action('em_booking_form_status_already_booked', 'em_booking_form_status_already_booked_custom',100);