How is I missed the train??

We will arrived in Shanghai Pudong on the 14 March at 07.00 am and would like to take a train from Pudong airport to Shanghai Hongqiao and continue from Shanghai Hongqiao to Changzhou North Station. Could I but the ticket online? What happened if I missed the train?? Can we rescheduled?? Or better I just bought when I arrived at Shanghai Hongqiao station? Please kindly advice.

Thanks and Regards,
Ariana