That will just come with time. Talk to them a lot in their cage so they can get used to your voice. Give them treats, especially when you take them out, and they will learn that coming out means great things.
A great technique for bonding is to put on a sweatshirt and just shove them inside it (between your shirt and the sweatshirt). They will feel safer being enclosed and they will be really close to you and get used to your smell, etc. Just as a tip: don't wear anything you treasure when you do this, as they might pee/nibble on it.
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Six new rats