How to use internal LFCLK on nrf5340 chip?

[likai]

Hi. I'm using nrf5340.  I confirm internal clock(LFRC RC osc) exist,I  want to remove external 32.768kHz X-tal. If yes, how can I turn on LFCLK RC oscillator in my source code? 

my ide is vscode，and SDK version is v2.0.0. example project's name is peripheral_uart.

Thanks.

[likai]

and more,V2.0.0\nrf\samples\bluetooth\peripheral_uart\prj.conf ,in this file,add the same configuration.resolved.

Thanks.