This is an old wound to the tree, that hasn't affected the tree negatively at this point. That you need to do now is to watch for further decay to that area. We do not recommend covering that area, as it is healed. If the area has or starts to decay, I would recommend contacting certified arborist for them to evaluate the tree and take their recommended steps to the tree. Likely, it would just removing that portion of the tree.
If you would like further information please see this link: https://plantpathology.ca.uky.edu/files/ppfs-or-w-01.pdf or contact your local extension office.