<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/Module/etc/module.xsd">
    <module name="Abc_Abc" schema_version="1.0.0" setup_version="1.0.0" >
        <sequence>
            <module name="Xyz_Xyz" />
        </sequence>
    </module>
</config>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="XyzXyzModelPaymentPaymentAbstract" type="AbcAbcModelPaymentPaymentAbstract" />
</config>

<?php
namespace AbcAbcModelPayment;

class PaymentAbstract extends XyzXyzModelPaymentPaymentAbstract
{
    public function getFormFields($order, $requestParams, $isRequest = true)
    {
        MagentoFrameworkAppObjectManager::getInstance()->get(PsrLogLoggerInterface::class)->debug("Works ");
    }
}