Second escalator, isn't it? That way you have to cross less streets. Which would make it:
Devonshire Street exit > tunnel > second escalator > walk straight ahead > cross road > walk straight to Tower Building...?
Or, you could always walk all the way down to the end of the tunnel, get the escalator up to the DAB Building, walk straight through and across the footbridge, and get to the Tower building that way. I always found that to be easier/faster than waiting for the traffic lights.
Whichever way you end up going, you're unlikely not to be able to see the Tower Building from the street.