Easiest way would be to just get CubeMX to configure it for you.
Even if you don't end up using the generated code in your final project, it will show you everything that needs to be done.
Otherwise, you will have to study the Reference Manual - that will have all the details of clock configuration, etc.
https://www.st.com/en/microcontrollers-microprocessors/stm32c051g8.html#documentation
A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.
