Working principle of the AD8232 high pass filter
HPSENSE - High-Pass Sense Input for Instrumentation Amplifier. Connect
  HPSENSE to the junction of R and C that sets the corner frequency of
  the dc blocking circuit.


HPSENSE is a negative feedback point for the instrumentation amplifier that processes the input and, if you connect the output of said IA to HPSENSE via a low pass filter (yes, that is what you analysed), the overall transfer function from the input of the IA to "the next stage" is one of a high pass filter.


  I would be happy if someone could explain me about how to get the cut
  off frequency and equivalent circuit of this High-Pass Filter


It is a low pass filter but, due to it being in the negative feedback path of an amplifier, the whole circuit performs as a high pass filter.