Actually you can linearize the system from any input and output pair you want. To do so, go on to signal, right click, go to Linear Analysis Points and select the input and output as Input Perturbation and Output Measurement respectively. Then, go to Analysis->Control Design->Linear Analysis and a tool will be opened. Now having the specified input and output for linearization, you can linearize the system and check its any kind of response, which can be Step, Bode or else. Hope this helps.