I would use super glue gel to glue the broken edges to a piece of base rock.
"scroll coral" is typically turbinaria reniformis...and care recommendations vary. I have mine in med-high light and medium flow. Keep the area around the coral free of detritus since the scrolling, vertical growth of the coral tends to promote detritus settlement...
Thanks, Dobish. The coral is actually an Oxypora sp. but I think your suggestion is a good one. I currently have the "pieces " wedged into crevices in the rock. If they don't stay put I will try the super glue.