如何更改HFCLK由微处理器上的低频振荡器控制？

I am using an EFM32G222F128 Gecko microporcessor made by Energy Micro. I am trying to make the current consumption of this chip to be as low as possible and to do so I want to switch the core clock to use the low frequency RC oscillator (LFRCO) instead of the high frequency one.I am using an EFM32G222F128 Gecko microporcesso