when try follow video on finetuning T5 on Question Answering

link: https://www.youtube.com/watch?v=r6XY80Z9eSA&list=RDCMUCoW_WzQNJVAjxo4osNAxd_g&index=1

when i run

53 trainer.fit(model,data_module) 
54         has_train_dataloader = is_overridden('train_dataloader', model) 
55         if not has_train_dataloader: ---> 
56             raise MisconfigurationException( 
57                 'No train_dataloader() method defined. Lightning Trainer expects as minimum a' 
58                 ' training_step(), train_dataloader() and configure_optimizers() to be defined.'

MisconfigurationException: No train_dataloader() method defined. Lightning Trainer expects as minimum a training_step(), train_dataloader() and configure_optimizers() to be defined

there has an error like this, how to fix it