How do I model an over voltage spike on LTSpice? Any circuit example
For a transient voltage spike you can click on your voltage source and under the advanced option choose the exponential output. Here you can provide the parameters for your spike such as the rise time and the fall time.

The absolute best method would be to construct a piecewise linear model (PWL).

In this, model you specify the voltage output at each time. Through linear interpolation the software will draw straight lines between these points and which will essentially construct your desired output.

A good reference:

LTspice Tutorial - Types of Sources - Voltage Sources - SFFM