Mount Frostbite and ride her to the source of the scent from Brann's note. Then, recover Brann's Communicator and use it to make contact with Brann Bronzebeard.
Boktar can have his way this time, but I'll expect him to make it up to me. Don't look at me like that. Boktar may be in command, but no one tells a hunter what to do.
'Put that beast away,' he says. 'Make it stop growling.'
All of a sudden he changes his mind when it suits him. Next time he complains, Frostbite'll just nip him a bit. Don't worry, she'll do an admirable job tracking your prey. After she locates her target, you're on your own to deal with iron dwarves, or Brann, or whatever you find.