The sorbate should have been bag #3 that came with the kit...if you've already done step 3, that's the step when you add the K-meta and sorbate, along with what ever clarifying agent they have included.
As far as flavoring it...I would wait until it's done clarifying, and then taste it. Depending on the kit, you may have another racking to "brilliantly shine" the wine. If that's the case you'll need to top it off again, then you can add whatever flavoring you like.
Personally I would just follow the instructions...unless one of the steps was really goofed up, the wine should be fine after a few months in the bottle.
Peace,
Bob