Oh, People have this problem a lot. Its actually really easy. All you have to do is reset the time (by pressing B while your tamagotchi isnt doing anything and then press A and C at the same time)to a time really late like 10:30 PM so your tamagotchi goes to sleep. Then set it back to regular time and the costume won't be there. Thats if you want it off right away. Other wise you can just wait until it goes to sleep and when it wakes up the costume will be gone.
ok, even though these kind of topics have been reapeatatly asked, the tamagotchi costume comes off as soon as it goes to bed. just simply set the time to 10:00 PM if you want the costume off. But, next time before posting a question, please search the forum using the search function for any simular topics instead of making a whole new topic.