1999 LS TheftLock Programming

I just bought a 99 Malibu LS with the TheftLock CD player. I do not know the code just in case the battery needs to be changed or whatnot. I do not have the owners manual eather.

I know there is a procedure to get the 6 digit code out of it. Can someone tell me how to do that. I already have the number to call and get a new code put in.

Thank you.