Don't reach in to bother a rabbit when he's in his cage. That's tip #1.
If he's lunging, I wonder if he's been neutered yet? If he has not, this can be a difficult time to try to bond with him. He'll be grumpy and hormonal.
As for bonding with a bunny in general... patience, and more patience. You start by ignoring them -- yup, ignoring them. But you ignore them as you sit in a confined area with bunny. Ideally, set up an exercise pen around the cage opening so bunny can hop out when (and if) he desires. Then, as he explores, you sit there and ignore him. If he approaches, great. Ignore him. This way he learns you are safe. In time, you will work up to petting up, but that will be after many days. Read
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