erp_hr_email_classes filter hook not working

following filter hook not working in hr emailer class.

file moduels/hrm/includes/class-emailer.php

/**
 * HR Email handler class
 */
class Emailer {

    use Hooker;

    function __construct() {
        $this->filter( 'erp_email_classes', 'register_emails' );
    }

    function register_emails( $emails ) {

        $emails['New_Employee_Welcome']   = new Emails\New_Employee_Welcome();
        $emails['New_Leave_Request']      = new Emails\New_Leave_Request();
        $emails['Approved_Leave_Request'] = new Emails\Approved_Leave_Request();
        $emails['Rejected_Leave_Request'] = new Emails\Rejected_Leave_Request();

        return apply_filters( 'erp_hr_email_classes', $emails );
    }
}

I add filter in my plugin but not working still get email on approved leave request.

add_filter( 'erp_hr_email_classes', 'my_register_email_classes' );
function my_register_email_classes( $emails ) {

unset( $emails['Approved_Leave_Request'] );
return $emails;
}

Actually I want to add new custom template tag in the approved email class. but I can find any hook to add custom template tag in the email.

**
 * Approved Leave Request
 */
class Approved_Leave_Request extends Email {

    use Hooker;

    function __construct() {
        $this->id             = 'approved-leave-request';
        $this->title          = __( 'Approved Leave Request', 'erp' );
        $this->description    = __( 'Approved leave request notification to employee.', 'erp' );

        $this->subject        = __( 'Your leave request has been approved', 'erp');
        $this->heading        = __( 'Leave Request Approved', 'erp');

        $this->find = [
            'full-name'    => '{employee_name}',
            'leave_type'   => '{leave_type}',
            'date_from'    => '{date_from}',
            'date_to'      => '{date_to}',
            'no_days'      => '{no_days}',
            'reason'       => '{reason}',
        ];

        $this->action( 'erp_admin_field_' . $this->id . '_help_texts', 'replace_keys' );

        parent::__construct();
    }