Instructions
Travel to Route 209, which is just outside of Hearthome City, or to Route 210, which is just outside of the Solaceon Ruins. Wild Chanseys are found in both these areas.
Walk in the tall grass until you encounter a wild Pokemon.
Capture a wild Chansey if you encounter her by attacking her with your Pokemon to lower her health bar in battle. Then throw a Pokeball at Chansey to capture her. If you do not encounter a wild Chansey, flee the battle by selecting "Run" and continue walking through the tall grass until you encounter a wild Chansey.
Select your wild Chansey from the "Pokemon" menu and then select "Summary." This will show you if the wild Chansey you caught holds a Lucky Egg. Continue hunting for other wild Chanseys if she does not hold a Lucky Egg.
Remove the Lucky Egg from Chansey by selecting her from the Pokemon menu and then selecting "Item" and then "Remove." You will now be able to equip the Lucky Egg to any Pokemon for an additional experience boost.