Ok so;
Go to your profile/ Press collections and choose a photocard/ Press the brush icon on the top right corner and decorate the photocard / When you're done, press the done icon on the bottom right corner (make sure it says that the decoration has been saved!) / Then, get back to your profile, find that photocard again and click it / Now, under the brush icon there is a pumpkin icon, from which you can enter the decorated photocard to the halloween event!
I hope this helped lol idk if I explained it properly 😭✨🤍