Hey this is unique challenge
Worst case scenario, universal control is rasp removal of any invader area, coral too, frag is controlled back to clean so those uninvaded corners can be spot fed and regrow
However
Possible to spot cure and lose only some coral.
That coral isn't hugely sensitive to light peroxide dilution work
If it's a green invader (seems red in pics)
Fluconazole diluted below norms in a container, set frag in container for a day etc. brainstorming test runs pending ID fluc is very restricted in receptives but where it works it works
The tricky balance is one method might work, and stresses the whole coral
One method certainly works, and you lose two thirds of the coral. Time is closing in on the healthy parts. If it was my frag it would be a blend: a knife and rinsing in saltwater uses tiny scrapes and digs would 100% debride the edges of coral and sides of disk of the invader so that your frag looks like a dentist worked it carefully
All the coral is left unharmed and as much cleaning by metal that could be done is done
Then for the overgrown coral parts, q tip in 3% peroxide application to target let sit cooking right about 40 seconds, rinse, put back, that's best chance lowest loss imo