How to set custom values for checkbox?

I want checkbox to have checked and unchecked values rather than true / false

As You mentioned, true / false are default values for checbkox.
If You want to set your own values u need to go properties of component then go to section Pozostałe. To change value of checked component You can use property “Wartość zaznaczonego przycisku” for unchecked it’s property “Wartość odznaczonego przycisku”.