Your Harmonica SuperStart card should have come with velcro already attached to the card, with another piece on top of it that is going to be placed on the harmonica.
As you can see in the illustration below, the velcro centers flat on top of the harmonica (the numbered side) but towards the back so the velcro doesn’t touch your mouth as you play.
In the illustration, the velcro is actually off the back edge of the harmonica a little bit, which is just fine – what matters is that the velcro is roughly centered on the harmonica so your SuperStart Card can join with it.
As mentioned in your book, the reason for your SuperStart card is that, when you line up the #1 hole on your harmonica with the circled #1 line on your SuperStart card, then all ten holes on the harmonica are lined up automatically and now you can actually see what you are playing.
Without your SuperStart Card, everything would be under your nose and there would be no way to know for sure where you are on your harmonica – so having your SuperStart card installed and ready to go on your harmonica is a really great thing – it will help you a lot!