Select the graph options for Power and Sample Size for 1-Sample Poisson Rate

Stat > Power and Sample Size > 1-Sample Poisson Rate > Graph
Display power curve
Plot the power of the test versus the comparison rate, with a curve for each sample size. Use this plot to compare the effect of different sample sizes.
Generate additional power curves based on
Enter sample sizes that you did not include on the main dialog box to display on the power curve.