Where is the thermostat on a 1993 Buick regal?

The thermostat on a 1993 Buick Regal is located under the intake manifold. This is a fairly involved job to access and replace, requiring mechanical skills and likely some specialized tools. It's not something easily visible or accessible without removing parts. You'll need a repair manual specific to that year and engine (3.1L V6, 3.8L V6, or possibly a different engine if it's a very unusual model) to properly guide you through the process.