Turn off power to the circuit at the breaker panel
Verify the outlet is de-energized with a voltage tester
Remove the outlet cover plate
Unscrew and pull the receptacle out of the electrical box
Check whether a grounding conductor is present in the box
If a bare or green ground wire is present, connect it to the green ground screw on the outlet
If the box is metal and properly grounded, add a grounding pigtail from the box to the outlet ground screw
If no ground wire is present, install a GFCI receptacle or GFCI breaker
Label the receptacle as “No Equipment Ground” if required
Replace the receptacle and cover plate
Restore power and test the outlet with an outlet tester
If unsure or if wiring is damaged, hire a licensed electrician