How to implement LSI in STM32CubeExpansion_LRWAN_V1.3.1 project instead of LSE ?

I am currently working on STM32CubeExpansion_LRWAN_V1.3.1 projects. I am using STM32l073 mcu.

In End-Node project, the LSE clock is used as RTC source. But I want to use the LSI clock as RTC source instead of LSE. So far I could not be succesful.

Could you help me about this issue? How can I implement the LSI clock correctly as RTC source in LRWAN project?