Sanding the reed will lower the pitch a bit. Extending the reed length a bit will make the call lower. Opening your throat will calling will help lower the note pitches. But, before you start messing with the guts, take a Sharpie pen, sharpen the tip a bit and make a mark across the reed, at the point the reed meets the wedge. Let it dry and that will serve as a reference point to help tune your call. The black line on the portion of the reed next to the wedge in the pic is that to which I am referring. the black line at the tip of the reed just shows where I have bent the reed tip up a little.
Note how close the reed tip is to the end of the tone channel. The closer it is to the end ..... but still able to be pushed into the tone channel ..... the less air required to run the call. You have to be able to push the tip of the reed into the tone channel or the call won't make a note. If you are concerned about the call being too high pitched to be effective ..... listen to some real geese talking .... listen to the geese on goose hunting videos, rather than the hunters on their calls. Real geese are mostly high pitched and that is what seems to be attractive to them and get their attention. If you have a place you can compare your goose call with the calling of real geese, take it there and run the call. You might be surprised how close the call sounds to them.
I tune my calls high pitched and yet I still will often have to bump up the pitch a bit when trying to match real geese. But, if you're working geese into the decoys, you still have to be able to make some low notes. So, you may need to tune the call so you a can make both, if you can't now get the low notes out of the call.