Add new value via entity cakephp 3

In CakePHP 3, you can add a new value to an entity using the following methods:

Using the newEntity() method:
```
$entity = $this->Entities->newEntity();
$entity->field_name = 'new value';
```
This method creates a new entity instance and sets the value of the specified field.
Using the patchEntity() method:
```
$entity = $this->Entities->patchEntity($entity, ['field_name' => 'new value']);
```
This method updates the existing entity instance with the new values.
Using the hydrate() method:
```
$entity = $this->Entities->hydrate(['field_name' => 'new value']);
```
This method creates a new entity instance and sets the value of the specified field.
Using the set() method:
```
$entity = $this->Entities->get($id);
$entity->set('field_name', 'new value');
```
This method updates the existing entity instance with the new value.

Note: Replace field_name with the actual field name you want to update, and $id with the actual ID of the entity you want to update.

Also, make sure to save the entity after updating it using one of the above methods:

$this->Entities->save($entity);

This will save the updated entity to the database.