is this code running inside the Task that is you data processing? Assuming it does check this code, it will fetch the pipeline and then the task you need

previous_task = Task.get_task(
        project=Task.current_task().project,
        task_name="process_dataset", #use "process_dataset" name from pipe
        task_filter={'status': ['completed']})

Notice using the current Tasks project and to make sure you are looking for a component running under the same pipeline