The best thing to do is to take your time!

Let him settle into his new home before trying to tame him, and let him see you fussing and treating the other one which will make him curious and see that you are not going to hurt him.

Another thing to do is place a raisin in your hand and slowly move towards him, when he gets agitated stop, and let him smell the treat. If he bounds off, leave him and try again the next day. If he only is able to get treats from your fingers he will soon learn and within a few days will start to approach you.

Some chinchillas are not very human-friendly and prefer the company of their own kind - and very few chinchillas enjoy being picked up and held. Trying to catch your chinchilla to put him bac in his cage will be stressing him - I would not let him out of the cage until he is more used to you

As your chinchillas are only young I would advise against letting them exercise out of their cage for more than a few minutes - some people do not let them out until they are 6 months old. Too much exercise at a young age can overheat them, and may cause fits.

Be patient - chinchillas can be highly strung and stubborn, but with time he will start to accept you.