how to filter related tables by date in larevel ?

I have 2 related tables, I need to filter the date of a table by month

My first table have the following fields: Id_agendamien_persona , Id_agendamiento, id_persona

The second table have the following fields: Id_agendamiento, fecha

so I need to filter fecha in the second table,

Mi controller

public function listar(){

        $contactos = Contacto::pluck('completo','id_contacto');
        $contacto_x_agendamientos =  Contacto_x_Agendamiento::all();
        array_add($contactos,0,"::Seleccione::");

        return view('agendamiento.listar')->with(compact('contacto_x_agendamientos','contactos'));

    } 

My model

first table

   class Contacto_x_Agendamiento extends Model
    {
        protected $table = "contacto_x_agendamiento";
        protected $primaryKey = 'id_contacto_x_agendamiento';
        const CREATED_AT = 'fecha_creado';
        const UPDATED_AT = 'fecha_modificado';

        public function Agendamiento(){
            return $this->hasOne(Agendamiento::class,'id_agendamiento','id_agendamiento');
        }

}

second table

class Agendamiento extends Model
{
    protected $table = "agendamiento";
    protected $primaryKey = 'id_agendamiento';
    const CREATED_AT = 'fecha_creado';
    const UPDATED_AT = 'fecha_modificado';


    public function scopeMes($query){
        return $query->whereMonth('fecha_agendar','=',date('m'))->get();
    }
}

View

<td></td>

error

Property [fecha_agendar] does not exist on this collection instance.

via Chebli Mohamed