Basically trees have the resources within to heal wounds. The best thing you can do is provide plenty of water and remove grass under the tree because it competes with the tree for resources. I would lay a soaker hose in concentric rings for easy watering. Also, mulch the roots out to the drip line with an undyed mulch such as arborist's wood chips. Here is an article that you can read. https://www.fire.ca.gov/media/5031/urbanforestry_water_wise_mature_tree_factsheet.pdf