First off I just want to state that when introducing a new chinchilla like that it's good to keep them in separate rooms the first three weeks. If the new chin for whatever reason has an infectious disease this minimizes the risks. I'm not saying that to be critical though but to point out a good practice.
Secondly most breeders recommend to introduce chinchillas slowly. You should put them in separate cages in the same room, at least 2" apart so they can't injure each other through the bars. Then just take care of them and interact for a 2-3 weeks. The new chin will be more comfortable with its environment. Then dust bath together and see how they do. If it doesn't work then repeat the cycle.
And don't be terribly disappointed if it doesn't work out. Not all chins are compatible with each other. Mine didn't like each other first. There was a big age difference and I tried to introduce them all at once. Today they don't live in the same cage but I let them together supervised and they normally do okay.
I discovered two problems. One is that the age difference was too much. The younger chinchilla was not settled down. It can take over a year for a baby chinchilla to act more civilized but they do settle down. The other problem is the older one is extremely dominant and the younger will take it for a little while and lash out when he's had enough.
Typically fighting is considered to be dangerous when fur is pulled out. If one ever gets bitten or bloodied do not ever try to reintroduce them as this is extreme aggression. Some chinchillas have been known to kill their cage-mates with one bite. Also be warned even a bonded pair can turn on each other unexpectedly with fatal results. It is rare but there are usually signs leading up to it. Also females can harder to pair than males.
Please remember this process can take months, not just days. Be patient and you might succeed.
