Greetings, Martin, and welcome to planDisney! As a Magic Key holder, I have lots of experience with the reservation system. Let's make sure you're all set for your trip!
Typically, when you successfully cancel a 
theme park reservation, you can make a new one right away, as long as your ticket is still valid and the date you are trying to reserve has availability. First, check your current reservations. Then, proceed as if you are making a new reservation – there, you should see how many reservations are available on your ticket.
On the 
Disneyland website:
    - Sign into your MyDisney account, hover over the "My Disneyland" tab, and select "Theme Park Reservations" from the dropdown. Click the "Make or Modify Park Reservations" button and scroll down to see your upcoming theme park reservations. Confirm that the one you canceled isn't there.
     - On the calendar, a slash indicates the date is not available. The pink castle represents Disneyland, and the blue icon represents California Adventure. Choose from an available date and proceed until you've confirmed your booking.
 
If you prefer to use the 
Disneyland mobile app, make sure you're signed in. From the bottom menu, tap on the icon with the three lines at the bottom of the screen (☰), and then tap "Future Plans." You'll see all your upcoming reservations. Or, from the bottom menu, tap the plus sign in the middle, and then, "Make a Park Reservation." From there, the process is essentially the same as on the website to check existing reservations and make new ones.
Following these steps, you should be able to make a new reservation. If you aren't able to do so, here are a few things to consider:
    - If you're using a single-day ticket, keep in mind that not all dates are valid for all ticket tiers. Lower-tier tickets have more blockout dates. If the date you want isn’t included in your current tier, you may need to upgrade your ticket.
     - Your desired date or park may no longer have available reservations – that would be indicated on the calendar with a slash. If this is the case, you may need to consider alternate days or check back later – additional reservations may become available as Guests modify their plans.
     - It's possible that your browser is experiencing an issue. I'd recommend restarting it, clearing the cache, or trying a different browser. You can also try the mobile app.
     - If you have a Magic Key and have gotten three no-shows within a 90-day period, you wouldn't be able to modify your theme park reservations for 30 days. However, that's specific to the Magic Key passes.
 
Martin, I hope this information is helpful to you. If you're still having trouble, you can try chatting with a Cast Member on the 
Disneyland website (make sure you're signed into your account and click the "Help" button on the right-hand side of the screen). Alternatively, there's a 
Tickets phone line that you can use (if you can make an international call). And, of course, you are welcome to reach out to us again for help if you need additional information.
Have a fantastic time visiting the Happiest Place on Earth, Martin!
Your pal,
Kriss