You can do this by observer.
SR/StackExchange/etc/frontend/events.xml
<?xml version="1.0"?> <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd"> <event name="customer_register_success"> <observer name="sr_customer_account_createPost" instance="SR\StackExchange\Observer\CustomerRegisterSuccess" /> </event> </config>
SR/StackExchange/Observer/CustomerRegisterSuccess.php
namespace SR\StackExchange\Observer; use Magento\Framework\Event\ObserverInterface; use Magento\Framework\Event\Observer; use Magento\Customer\Api\CustomerRepositoryInterface; class CustomerRegisterSuccess implements ObserverInterface { /** @var CustomerRepositoryInterface */ protected $customerRepository; /** * @param CustomerRepositoryInterface $customerRepository */ public function __construct( CustomerRepositoryInterface $customerRepository ) { $this->customerRepository = $customerRepository; } /** * Manages redirect */ public function execute(Observer $observer) { $accountController = $observer->getAccountController(); $customer = $observer->getCustomer(); $request = $accountController->getRequest(); $customer_number = $request->getParam('customer_number'); $customer->setCustomAttribute('customer_number', $customer_number); $this->customerRepository->save($customer); } } NB: here 'customer_number' is custom attribute