Adding text to record field

Hi!

I need to add text to record (NOT OVERWRITE). This is my code, but it's overwriting to field 8, and I don't know why.

CONTROLLER:

PHP Code:

    public function ServiceDecline( $id = "" ) {

        $id = array( 'id' => $id );

        $UserID = $this->ion_auth->user()->row();

        $DeclineList = $this->AdminServices_model->DeclineList();
        $DeclineList = array_push( $DeclineList , $UserID->id );

        $AddDeclined = array( 'odrzucili' => $DeclineList );

        $this->AdminServices_model->DeclineService( $id, $AddDeclined );
        
    } 


MODELs:

PHP Code:

    public function DeclineList(  ) {
        $query = $this->db->get( 'services' );

        return $query->result();
    } 


PHP Code:

    public function DeclineService( $id, $AddDeclined ) {
        if ( $this->db->update( 'services', $AddDeclined, $id ) ) {
            $this->session->set_flashdata('msg', 'Success!');
            redirect( 'service/zgloszenia' );
        }

    }