The quick launch button for UVI-Extract is located at the bottom of the "File Browser" window in the Mach-5 module, and is labeled UVI Extract. The "File Browser" is located in the upper left-hand portion of the Mach-5 module.
When you click this button it will launch the UVI extract application and allow you to convert samples. After converting Mach 5 will rescan samples and recognize the new patches when you select the appropriate soundbank, so there is no need to relaunch or close the application.