Oh, Arnold! I'm absolutely heartsick for you! I know you can't imagine a worse thing, so let's see if there's anything you can do to get sorted out.
Walt Disney World does require
theme park reservations, as you obviously know. In order to swap one theme park for another - like
Disney's Animal Kingdom for
Disney's Hollywood Studios - you have to cancel the reservations you actively have and rebook from scratch. Unfortunately, in your case, you're visiting at one of the busiest times of the year, and people are trying super hard to watch the
theme park reservation availability calendar to snag a cancellation - like yours.
The first thing I am going to recommend is that you
get on the phone as soon as you can with Guest Services. The phones are super busy right now, but if you can call as soon as they open at 7 AM or try close to the 11 PM closing time, your wait may not be as long. If there's anything that can be done, they may be able to help.
Do you have
Park Hopper tickets, by any chance? If you do, you can make your theme park reservation for the morning at ANY of the parks with availability. Scan in there, then after 2 PM you can hop to the park you really want to be in. You can even use
Disney's Genie+ at the second park, so you can still plan to do some of the attractions you are hoping to do.
Try Guest Services first, Arnold. I'll be sending you all the pixie dust and positive thoughts!
Anna