Can't they see (hear) through the bifrost, or it has its own sensing abilities. Heimdell was not operating the bifrost in ragnarok, but the remote call from Thor was still heard in the bifrost room.
They can probably open the portal to "Earth", and from that determine the location of the fight, or possibly of his avenger friends, or even vision's stone and the precisely direct (except Heimdell who had "the sight").
When they use the bifrost they always appear at precisely the correct place, how could they know where Jane is when he pops by to see her in the dark world, they probably see earth then can pinpoint to specific places after that.
Or like Heimdell, maybe having control of the bifrost gives you "the sight" to see where you want to go before you go there.
But I'm not a bifrost engineer, so who knows, maybe it's just good screenplay writing where something important happens at precisely the correct time.