It's F8 key for tempo

There are videos available for setting tempo in ACW
You can always change the chords later, so the Chord part in Audio Chord Wizard can be misleading. Yes it does make the original 'guess' at the chords for you. But remember, you can always change them later using the Chords window, so the real power is in the Tempo aspect.

Once you have the tempo locked you can change the chords at will in the regular RB interface.
It's the Tempo feature that makes the ACW so cool.
I understand marketing-wise the chord feature is stronger, but in real use, I find the Tempo feature more valuable as it allows the Chords window to do what it does along with the song. Which means it enables the ability to generate tracks in time with prerecorded audio.

Actually, I wish when it did it's initial popup asking about keeping the existing tempo map, it defaulted to 'No'. I never want that when I use the ACW.

I do not work here, but the benefits are still awesome
Make your sound your own!