Included with the mouse should be small clear plastic square spacers with numbers indicating the thickness from 0.5mm to 0.8mm.
These were included so you can customize the button click feel of each button set. You can do this by using a knife or small thin flat tool to pry off the small clear plastic spacer under the button trigger then replace them.
Try 0.8mm for M1 and 0.7mm for M2 to reduce the pretravel. Change the M2 button to 0.6 mm and screw the screws at the bottom of the button cover to make it feel less stiff.
Soft & Subtle
Light & Soft
Light & Crisp
Crisp & Tactile
Here is a tutorial video we made to reduce M2 pretravel: