If you already have an in-person reunion posted on the Classmates site, you won’t be able to switch it to a virtual one (or vice versa). However, you can create a new virtual reunion following the instructions found here.
Once you’ve done that, you can update the details on your original reunion to let invitees know about the new virtual one. Keep in mind that everyone on your Class List will automatically be invited to the new virtual reunion you created!
If you have both event types posted, you’ll be able to edit and manage the events separately, and your class will see each event in their Reunion Center, which can be found by clicking Menu in the orange bar at the top of any page and selecting My Reunions.