If you only need simulation without a 3D model, you can download the LM2596 SPICE model directly from Texas Instruments. This model can be integrated into Proteus as a VSM (Virtual System Modeling) component. How to Install the LM2596 Library in Proteus
To manually add the LM2596 component to your Proteus software, follow these standard steps: lm2596 library for proteus top