hi
from support
"You may ask us to delete this giveaway. You need the winner's permission. Please ask them if they agree to delete this giveaway. If so, take a screenshot of the chat, upload it to imgur, then click on "Delete Giveaway" in the left column of the giveaway page and link your screenshot in the Description field. You could also ask the winner to leave a comment on the giveaway page stating they are ok with having the giveaway deleted."