by transient response I'm assuming you mean impulse response?? - use a square wave signal as input (VPULSE), and set the pulse width to be extremely low compared to your period, so as to simulate a delta spike.
step response - also use VPULSE input, and set the period to be long and the pulse width to be almost as long (say, 99% of the period), so that it simulates a unit step funtion
your outputs in each case will be periodic, but within one period of your output you will be able to see your step response and impulse response
in each case, use the Transient setup