How do you fix tree damage?
When a tree is wounded, the injured tissue is not repaired and does not heal. Trees do not heal; they seal. If you look at an old wound, you will notice that it does not “heal” from the inside out, but eventually, the tree covers the opening by forming specialized “callus” tissue around the edges of the wound.
Research indicates that wound dressings (materials such as tar or paint) do not prevent decay and may even interfere with wound closure. Applying wound dressings are not recommended. Trees, like many organisms, have their own mechanisms to deter the spread of decay organisms, insects, and disease.
Conclusion. Healthy trees usually recover from wounding quickly. Try to keep wounded trees growing vigorously by watering them during droughts and providing proper fertilization. This will increase the rate of wound closure, enhance callus growth and improve the resistance to decay mechanisms. (source: https://agrilife.org/treecarekit/)