External task id and complete

Hi . i have two process running completely in async mode. i am trying to complete external task using just the externalTaskid. but looks like there is no setId method before i complete
externalTaskService(externalTask,variables)

idea is i will someway get the externaltaskID and i want to use .complete but not sure how can i set the externalTask id before completing
vish

i am getting the below error

@RequiredArgsConstructor
@Slf4j
@Component
public class ClassA{

private final Logger logger = LoggerFactory.getLogger(ClassA.class);
private final ExternalTaskService externalTaskService;

****ERROR
error: variable externalTaskService not initialized in the default constructor
private final ExternalTaskService externalTaskService;

not sure what is that i am doing wrong, any pointers would help

Can you explain exactly what you’re trying to do?
Are you trying to create an external task client in Java to complete work for a BPMN process?