To find it, you'll likely need to:
1. Locate the fuse box: This is usually under the dash, on the driver's side.
2. Look closely around the fuse box: The hazard flasher relay is frequently very close to it, sometimes even part of the same assembly.
3. Consult your owner's manual: Your owner's manual should have a diagram of the fuse box and relay locations. This is the most reliable way to pinpoint it.
If you can't find it easily, a search online for "1991 Buick Regal hazard flasher relay location" with images might provide visual clues. Remember to disconnect the negative battery terminal before working near electrical components.