The decrease length is built into the Wave Function Sketcher.
Set up a situation similar to Figure 9 below.
For each of the regions you can select "Oscillating" or "Decreasing" for the wave function. Using the decreasing options, use the program to sketch a wave function that is acceptable for this situation.
Make a sketch of the wave function as displayed by the program. You may like to print the graph below and use it to make your sketch.
Make the wave function smooth by changing the amplitude and phase for each region.
Sketch the probability density for the electron. Write a brief paragraph of interpretation for this wave function below: