change-username-social-login.php

/**
 * Customize user data for new users registered via WC Social Login
 * Example: set a custom role other than "customer" on registration
 */
/**
 * Add filters to adjust user data for each active Social Login provider
 */
function sv_wc_social_login_new_user_data_add_filters() {
	if ( ! function_exists( 'wc_social_login' ) ) {
		return;
	}
	foreach ( array_keys( wc_social_login()->get_available_providers() ) as $provider ) {
		add_filter( 'wc_social_login_' . $provider . '_new_user_data', 'sv_wc_social_login_new_user_data' );
	}
}
add_action( 'init', 'sv_wc_social_login_new_user_data_add_filters', 100 );
/**
 * Filter the new user data on registration via Social Login
 *
 * @param array $user_data the data set for the new user at registration
 * @return array the updated user data
 */
function sv_wc_social_login_new_user_data( $user_data ) {
	$first_name = $profile->get_first_name();
	$last_name = $profile->get_last_name();
	$user_data['user_login'] = $first_name.$last_name;
	return $user_data;
}