Instructions
Insert your copy of "Pokemon HeartGold" into your Action Replay DS. Insert the Action Replay DS into the game slot on your Nintendo DS.
Turn on your DS and select the DS Action Replay device icon in the main menu.
Select the "Code Select" option in the Action Replay's main menu. Select the "Add New Code" option in the next menu.
Enter the name of the code in the text box of the name entry screen. You can enter any name you wish, but a name that identifies the code, such as "Catch Trainer's Pokemon," is preferable.
Enter the following in the text menu of the code entry screen:
9224670A 00002101
1224670A 00002100
D2000000 00000000
Select the "OK" option to return to the code select screen, and select the "Catch Trainer's Pokemon" code.
Press the "Start" button to begin playing. As long as the cheat is activated, you will be able to catch the Pokemon of other trainers.