Chat with Support and reference this article. 

Please include the following information:
  1. The event name and URL that the participant will be moved from
  2. The event name and URL that the participant will be moved to
  3. The name of the Virtual Account  that the participant will be moved from
  4. The name of the Virtual Account  that the participant will be moved to
  5. The Supporter ID and Payment ID for the participant to be moved
  6. Indicate whether the participant has any donations credited to them for the event