Why not? What happens? Which calendar app are you using?

 

Is this app synced to some account (Google, Samsung, Outlook or something else)? If so you just need to set up the same account on the new phone.

If you have been storing local, non-synced events on the old phone you will need some way of backing them up on the old phone and restoring them on the new one. So knowing what app you are using, what sort of events and how you are trying to do this is necessary before anyone can try to answer the question.