Whenever this happens, it is best not to panic. Placing the serum you put on your gecko may contain other chemicals that are not healthy for reptiles. Please only use products that have been proven to effectively help reptiles or are made specifically for reptiles. Also, reptiles tend to have the best coagulating blood in the animal world. Yes, there may have been some blood, but it stops rather quickly without complication. To keep this wound clean and able to heal, please follow these steps.
1. Get a shallow container and fill it with warm water. Mix some betadine into the water until it is the color of a weak tea.
2. Place the gecko in the container and gently wash that scabbed area of the gecko with the mixture.
3. Rise the gecko in clean water.
4. Place a small dab of Neosporin antibiotic ointment on the wounded area. Make sure it does not contain painkillers or numbing agents as this can kill your gecko.
5. Repeat these steps every 2 days until the wound looks healed. That area of skin will likely never look the same, but it will return to look more closely like it did before the wound.
6. Tip: if the gecko is on a loose substrate (sand, wood, etc.) it is best to remove and use paper towels until the wound in fully healed.