To find it, you'll likely need to:
1. Consult your owner's manual: This is the best place to start. It will have a diagram of your fuse box and relay locations.
2. Check the fuse box: The fuse box itself usually has a diagram on its cover indicating what each fuse and relay controls.
3. Look for a relay that's roughly square and about an inch in size. It will likely have markings indicating its function (although it might not explicitly say "hazard flasher").
4. If you can't find it under the dash, there's a slight chance it's in the engine compartment fuse box. This is less common but still possible.
If you're not comfortable working on your vehicle's electrical system, it's best to take it to a mechanic. Incorrectly handling relays can potentially damage your vehicle's electrical system.