I assume your new iguana rejects being handled. He may also be so depressed and fearful that he lets you pick him up without any outward reaction. That is abnormal behavior.
You are asking a very basic question. I have to say, for the best for your iguana, that you haven't done much research about captive iguanas. This topic is very detailed, and your iguana can' survive unless you do the reading. This is likely the best iguana care info on the internet:
Read all of it, but also scroll way down to Picky Eaters and read that first.
Even a one page care sheet will say that iguanas don't eat after big changes in their lives. I have no idea yet of how accurately made your ig's habitat is. It might be great, I just don't know.
There might be info that is as good, but there is none better.
What is most likely happening is your ig is suffering from change-related stress. During this state, they don't eat, drink, behave, or bask right. They also don't display their real personalities, and often seem more tame than they really are. The appearance of feisty (even defensively biting) behavior is a sign of a big step toward recovery. If it's vivarium is well planned, it will recover in 3 to 4 weeks, hopefully sooner. In the meantime don't do anything extreme to make him eat.
Stress-related problems often lead to intestinal illnesses (he may get a tummy-ache), and the ig will need to see an exotics vet to get it's hind-gut fermenting digestive system working right again, and to get re-hydrated.
At 3-4 weeks of non-eating, igs become dehydrated, which is an illness unto itself. (They get a lot or most of their daily fluids from their food.) Feeding water with a dropper can turn this around, but sometimes they need IC fluids to really beat the dehydration.
Use a small clear-glass bowl of water and float a piece of lettuce on it every day. I can help him notice standing water.
Don't handle him at all for 3 to 4 weeks.
For now, make sure he has good basking temperatures, and a good cool-side temperature. Also make him a hide box that he can get all the way into so he feels hidden. Hopefully he will use it, and he might spend lots of time in it. Sometimes igs recovering from this kind of stress first come out only at night, and they might eat and drink at night. So put out some fresh food/water every evening before you go to bed.
Please do keep us informed about his progress. We are a non-judgemental community, so you will never be attacked or flamed.