使用自定义付款方式付款时如何更改订单状态 - Magento 2

Im using:

self.placeOrder()

to create a payment order in magento 2 by a custom payment method.

Everything works ok, but i need to change this status to another.

I tried changing system.xml in magento 2:

                <field id="order_status" translate="label" type="select" sortOrder="20" showInDefault="1" showInWebsite="1" showInStore="0">
                <label>Status no Pedido</label>
                <source_model>Teksystem\Pagamento\Model\Config\Source\Order\Status\Pendingpayment</source_model>
            </field>

to

                <field id="order_status" translate="label" type="select" sortOrder="20" showInDefault="1" showInWebsite="1" showInStore="0">
                <label>Status no Pedido</label>
                <source_model>Teksystem\Pagamento\Model\Config\Source\Order\Status\ Newprocessing</source_model>
            </field>

and change the status...

but magento does not see this status modification. I think want to do something on placeOrder method but dont know how.