I am sorry to hear this. Sadly theres very little you can do , Tangs are very argumentative fish and seldom get on with each other. Depends how big the tank is too. As I have always been lucky with having big tanks I never get just one fish,it helps. There will be some bullying with any new fish .If theres one agressor I often say stick it in the sump for a few days .
I do hope things turn out well and I am sorry I cant be more positive,one thought,can you keep the lights off for say 24 hours ? Some times this works.