Larry's given good advice. When I have a call that isn't quite deep enough in pitch, I start by lengthening the reed since it's the easiest thing for me to adjust. I simply slide the reed out a tad and try the call again. Doing this, I can see how much longer the reed needs to be before I start cutting up new reeds. To get more rasp, I'll start by cutting larger dog ears on the reed.
If the above approaches don't get me the sound I'm after, then I start filing on the toneboard, lengthening &/or deepening the tone channel, etc. But, it's awful hard to put wood back on once you've filed it away. That's why I start with the reed.
Be sure you take notes of what you try and what the outcome is. Whether results were good or bad, those notes will help you on future calls.