Several ways to do repairs.
Make a paste of kiln wash and push it into the divot. lightly sand to smooth. It will have to be re-done periodically.
Make a paste of cement fondu, smooth it while wet, because it gets hard when cured. Cure by firing in kinl to about 720C
Make a paste of cement fondu and vermiculite. Treat it the same way as cement fondu on its own. This combination holds less heat than cement fondu on its own.