Answer: It has been a couple years since that nasty freeze and by now your ficus will have compartmentalized the damage and sealed it off from the live tissues in the trunk. There's really nothing you can or should do. Any foreign matter such as tree seal can actually hold too much moisture against the bark and inner tissues and cause more damage than if you just allowed the tree to callus over the wound. It will, eventually. In the meantime try not to get the area wet with water from the hose. Best wishes with your landscape.
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