If no one is bothering the Flame, leave him with the other fish and feed the tank as usual. If it is in good health it will come around and start eating, watching the others eat. If you move the Flame to another tank you are increasing the stress level in the fish and will take longer to start eating. I always try frozen brine shrimp and if hungry they will go for it.
I also ask the LFS to feed the fish before buying it, make sure it swallows the food not spit it back out.
Best of Luck with your Flame angel hope it start to eat. I have a small Flame and it pigs out at feedings, just be patient.