You'll need to consult your owner's manual for the exact location of both the fuel pump relay and the fuse that controls the relay's circuit. The owner's manual will have a fuse box diagram showing the fuse and relay locations.
The fuse might be labeled as something related to the fuel pump, the engine control system (ECM), or a similar function. It's typically located in either the under-hood fuse box or the interior fuse panel (usually under the dash).
Without your owner's manual, I cannot provide the exact location. Searching online for "2000 Chevy Blazer fuse box diagram" may provide a diagram, but ensure it is specifically for the 4.3L Vortec engine to get accurate information.