I understand you're looking for software for the (often referred to as the Xir P3688 or part of the XiR P3600 series ). However, I must provide a critical heads-up before proceeding:
It is not legally available for free from official sources. Downloading it from unauthorized third-party sites (torrents, file-sharing forums, etc.) is software piracy, may expose your computer to malware, and can permanently damage your radio if the wrong codeplug or firmware is used. Motorola Xir P3688 Programming Software Free Download