Double-click setup.exe to run the Boot Camp installer.
The downloaded BootCamp5.1.5621.zip file (Ensure you download it from official Apple sources to avoid malware). Step-by-Step Installation
Following the on-screen prompts and restarting the system to finalize driver installation. Common Issues
: Without more context, it's challenging to pinpoint exactly what 515621 refers to. Product numbers or specific codes can relate to a variety of things, including but not limited to specific hardware models, software versions, or particular support articles. If you're looking for support or specific software related to this number, I recommend checking Apple's support website or contacting Apple Support directly.