I don't know what you mean. We saw Loki immobilize Heimdall with the Casket Of Ancient Winters and take control of the bifrost, and let Laufey and his soldiers in that way. It was only by the end of the film that the bifrost got wrecked.
Or are you referring to how Loki secretly aided the other frost giants early in the film, to get entrance into the weapons vault without the bifrost? That's something to be answered in future films. Loki does tell Heimdall there are secret passages between the worlds that even Heimdall, with his all-seeing sight, are unaware of. I believe Odin knows about them too, but has concealed that knowledge to keep all traffic on the bifrost.
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"I'm not smart so much as I am not dumb." - Harlan Ellison