1. Small mistakes, such as spelling mistakes or punctuation mistakes, can be corrected directly on the original billboard. This can be achieved by sticking stickers to correct mistakes or using spray paint.

2. If the mistakes are serious, such as the words or pictures on the billboard are wrong, it may be necessary to re-create the billboard. This may take some time and cost, but it can ensure the accuracy of the billboard.

3. For some large billboards, professional construction teams may be needed to transform them. This may involve aerial work, so you need to be extra careful.