It is import too understand the the 2nd step does not say "believed" (past tense) is says "came to believe". This is a process, not a singular event. You do not have to have a concrete idea of your HP to proceed, just a willingness - as many have pointed out - to believe in a power greater than yourself.
As you works steps 3 thru 9, your understanding of yourself, your addiction and your Higher Power will be profoundly different than it is right now. THIS is the process step 2 talks about "came to believe".
Even if you feel you don't truly believe, just try it, you have nothing to lose.