Change LCD contrast on Pico GFX Pack

Hello all!
I’d like to have possibility to change the contrast of LCD display on GFX Pack.
In st7567.cpp I see that default contrast level is 30
“if(auto_init_sequence) {
command(reg::BIAS_1_7);
command(reg::SEG_DIR_NORMAL);
command(reg::SETCOMREVERSE);
command(reg::DISPNORMAL);
command(reg::SETSTARTLINE | 0x00); //Startline from 0x40-0x7F
command(reg::POWERCTRL);
command(reg::REG_RATIO | 4);
command(reg::DISPON);
command(reg::SETCONTRAST);
command(30); // default contrast level
}”
What do I need to do to change this default value?