Anyone know how to fire heavy weapon on a daydream be headset?

The default controller is quite limited, so you will need a third party controller (like a MOGA or some such) to be able to fully control your ship. I do not know how the buttons are bound by default, but if you have a primary fire button (on top of auto fire) you can put all guns in the primary fire group (see weapon groups in ship > configure), rockets and missiles will not auto fire, so if you have a primary fire button, you can use it to launch missiles. Obviously the power drain will increase if you are firing small and large port energy weapons at the same time, so take that into consideration when aiming for a shot.

Best bet is to get a different controller though.