One has to prepare for the exam if registered, till the CFA Institute or Prometric sends an email of exam cancellation. If due to Covid, the exam gets cancelled and you receive such email, they will register you automatically for the next exam, though you should keep in touch (inform) with the Institute via email. In this case, you will not be charged any fees.
For purposeful deferral request please see the below thread.
February 2022 candidates: The deferral request form will be available on 12 January 2022 through 15 March 2022 at 5:00 pm ET.