Start by importing your diving board model into Simscale, then create a new frequency analysis simulation.
View the results in Simscale. The "Eigenfrequencies" plot shows the different frequency vibrations for the different mode shapes. The first eigenfrequency is the one that is considered the "fundamental frequency", so the goal is to get that to be 55 Hz. You can view the different shapes by changing the "time" option on the top toolbar.
HINT: Changing the geometry of the board will change the resonant frequencies linearly.