“wpcargo_add_form_fields” hook is used to add a custom field in the track form.

function my_custom_form_field(){
	?>
<td><input class="input_track_num" type="text" name="wpcargo_receiver_name" value="" autocomplete="off" placeholder="<?php echo apply_filters('wpcargo_tn_placeholder', esc_html__('Enter My Custom Field', 'wpcargo' ) ); ?>" required></td>
<?php
}
add_action('wpcargo_add_form_fields', 'my_custom_form_field', 20);