change date format to a datefield?

Add in beforeSave:

// if it's already DateTime object:
$this->date = $this->date->format('d/m/Y');
//if not create one:
$this->date = (new DateTime($this->date))->format('d/m/Y');

How do I set my function for variables? $CONT_FECNACI; $CONT_FECINSC

this is my model <?php

class SpmContacto extends \Phalcon\Mvc\Model
{

public $CONT_CODIGO;
public $CONT_CEDULA;
public $CONT_RUCIDE;
public $CONT_NOMBRE;
public $CON_ESTADO;
public $CONT_TELEFO;
public $CONT_DIRECC;
public $CONT_AREA;
public $CONT_CARGO;
public $CONT_TIPOXX;
public $CONT_EMAIL;
public $CONT_USUARIO;
public $CONT_CLAVE;
public $CONT_CLAVEE;
public $CONT_FECNACI;
public $CONT_FECINSC;
public $CONT_TIPOCODIGO;

/**
 * Initialize method for model.
 */
public function initialize()
{
    $this->setSchema("SPOLS");
    $this->hasMany('CONT_CODIGO', 'SPMREFERENCIA', 'CONT_CODIGO', array('alias' => 'SPMREFERENCIA'));
    $this->hasMany('CONT_CODIGO', 'SPTDETALLE', 'CONT_CODIGO', array('alias' => 'SPTDETALLE'));
    $this->hasMany('CONT_CODIGO', 'SPTENCABEZADO', 'CONT_CODIGO', array('alias' => 'SPTENCABEZADO'));
}
public function getSource()
{
    return 'SPM_CONTACTO';
}
public static function find($parameters = null)
{
    return parent::find($parameters);
}
public static function findFirst($parameters = null)
{
    return parent::findFirst($parameters);
}

}

Just add:

public function beforeSave()
{
    // do something with $this->CONT_FECNACI
    // do something with $this->CONT_FECINSC
}

to your class SpmContacto

I add the following

 public function beforeSave()
{
    // if it's already DateTime object:
    $this->$CONT_FECNACI = $CONT_FECNACI->date->format('dd/mm/YYYY');
    $this->$CONT_FECINSC = $CONT_FECINSC->date->format('dd/mm/YYYY');

}

but the result was:

500 Internal Server Error

So just check the log. You just added hell a wrong code. First learn php before using any framework beacause it looks like you don't even know plain php and OOP etc.

No, I do not know all PHP commands, so I'm learning. It is the first really to work with a framework. But not knowing is no reason not to learn

Yes it's reason good enough to not learn FRAMEWORK. For first learn PLAIN PHP and object and OOP. For isntance:

$this->$CONT_FECNACI // there is no $CONT_FECNACI variable in beforeSave() function
$this->$CONT_FECINSC // there is no $CONT_FECINSC variable in beforeSave() function
$CONT_FECNACI->date->format('dd/mm/YYYY'); // there is no $CONT_FECINSC variable in beforeSave() function, also are you sure that $CONT_FECNACI have property with name date ?
$CONT_FECINSC->date->format('dd/mm/YYYY'); // there is no $CONT_FECINSC variable in beforeSave() function, also are you sure that $CONT_FECNACI have property with name date ?

Those problems are not framework related. You just wrote wrong code and you could wrote it in any framework. First learn plain php, objects, classes etc - then start with framework.

Thank you very much for your help and have a different result continuare consulting

public function beforeSave()
    {
    $CONT_FECNACI = (new DateTime($CONT_FECNACI))->format('d/m/Y');
    $CONT_FECINSC = (new DateTime($CONT_FECNACI))->format('d/m/Y');
    }

DateTime::__construct(): Failed to parse time string (25/04/2016) at position 0 (2): Unexpected character

You already have 25/04/2016 so it's d/m/Y ?