How do you reset the pokewalker for Soul Silver?

I accidentally deleted my old game before taking my pokemon from the pokewalker. I don't want the pokemon, I just want to be able to use the pokewalker with my new game. I've tried the down arrow + X + L, but it doesn't work for me for some odd reason. How long do you have to hold that down for? Is there any other way to reset it?