To model decoupling capacitors in HyperLynx Power Integrity, you can utilize the Advanced Decoupling Simulation feature, which allows you to simulate the effects of capacitors on your Power Distribution Network (PDN). This involves specifying capacitor values (including ESL and ESR) and selecting the relevant power and ground nets. You can then choose the power pin pairs from a provided table and run the simulation to analyze the impact of the decoupling capacitors on the PDN's impedance.