Take the butterfly carefully and put it somewhere safe and quiet. As little force as possible, use a soft brush or fingers to keep the damage from getting worse.
Find out how bad the damage is. It might not be possible to fully fix the wing if it is torn or missing parts.
For small tears, you can fix them with a small amount of safe glue, like PVA glue. Use a stick or a fine brush to put it on, and then gently press the wing to keep it in place.
Use a small piece of paper or tissue to support the wing while the glue dries. This will help it keep its shape. Put the piece of paper under the wing and fold it over it slowly.
In a warm, dry place, let the glue dry all the way. It could take hours to do this.
You can let the butterfly go back to its home once its wing is dry and it seems to be moving properly.
It is important to remember that butterflies with broken wings may not be able to fly for long. Giving them a safe and helpful place to be can give them the best chance.