class_docstr: Example messenger onboarding world for chat task, displays intro and explains
  instructions.
class_docstr_tok: ["Example","messenger","onboarding","world","for","chat","task",",","displays","intro","and","explains","instructions","."]
code: def assign_roles(agents):
      for a in agents:
          a.disp_id = "Agent"
  
imports: from parlai.core.worlds import World
  from parlai.chat_service.services.messenger.worlds import OnboardWorld
label_desc: Use image node_id 3 for calling the MessengerChatOnboardWorld obj's underlying member method code with example usage: obj.assign_roles(agents) without return types