Hey there! So, on your initial roll, you can't roll a 7. However, this uses the Push system. By design, in the Push system, when you roll a 4 or lower on your d6, it's a weak hit—but you can choose to roll an additional 1d6 and add it to that result. You have to add that value, even if it pushes you over 7 and turns it into a miss. Think of it as a risk vs. reward—eat the weak hit, or take a risk to see if you can push it into a strong hit, but it might also become a disastrous miss.
I hope this helps! If not I can diagram out a few rolls for you.