entity code:

<?php
namespace App\Model\Entity;

use Cake\ORM\Entity;
use Cake\Utility\Inflector;
/**
 * Pet Entity.
 */
class Pet extends Entity
{

    /**
     * Fields that can be mass assigned using newEntity() or patchEntity().
     *
     * @var array
     */
    protected $_accessible = [
        'petname' => true,
        'ownerid' => true,
        'petowner' => true,
        'species' => true,
        'sex' => true,
        'ostreet' => true,
        'odate' => true,
        'ocheck' => true,
        'dogpic' => true,
    ];
    
    protected function _setPetname($petname)
    {
        $this->set(strtoupper($petname));
        return $petname;
    }
    
    
}

controller code:

public function add()
    {
        $pet = $this->Pets->newEntity($this->request->data);
        //////WHERE DO i SET THE VARIBLE $petname AND HOW DO I CALL THE SETTER AND DO I
        /////NEED A GETTER AND A SETTER?  MANUAL DOES NOT EXPLAIN WHAT TO DO.
        
        if ($this->request->is('post')) {
            if ($this->Pets->save($pet)) {
                $this->Flash->success('The pet has been saved.');
                return $this->redirect(['action' => 'index']);
            } else {
                $this->Flash->error('The pet could not be saved. Please, try again.');
            }
        }
        $this->set(compact('pet'));
    }