how to reduce clockspeed?

[BIBA.BUTZEMANN]

Hi guys, whish you a nice 3rd advent !
I tried to reduce cpu clock-speed for saving power but without success - whats wrong??
Compiling and downloading is possible but with no affect:

void setup(){
#define APB_CTRL_PRE_DIV_CNT; //Cpu-speed 8mMHz / 2 = 4MHz; //HB
#define RTC_CNTL_SOC_CLK_SEL;
APB_CTRL_PRE_DIV_CNT(2);
RTC_CNTL_SOC_CLK_SEL(0x2);

I use ESP32 with Arduino IDE and Windows10
Thanks
BIBA