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Firstly you need to be sure the model you are using has flicker noise modelled.
Do the usual noise analysis from say 0.1Hz to a high frequency. Zoom in the low frequency portion of the Noise Spectral Density(NSD) and see the noise behaviour. You can use the noise summary if you are using spectre. If the flicker noise is modeled, you will see the NSD dropping from 0.1Hz to a few 100Hz or Khz and then becoming flat.
the noise corner frequency tells you what dominates at what frequency. Below the corner frequency flicker noise dominates and after that thermal noise.
If you are looking for an automated setup, you can ask the simulator to find the thermal noise spectral density first, which is fairly constant over the entire bandwidth of measurement. So large frequency noise is thermal noise. Then subtract this NSD from the total NSD. The remnant will give you an idea of flicker noise and also corner frequency.
Not sure if this is exactly what you are looking for.