Fastferment Bottling Question

I am ready to bottle my beer and I have a bag of sugar that came with my kit that I have to add before I bottle. Do I add it to the Fastferment and stir until dissolved then add beer to bottles and cap or do I add the sugar to the bottle and fill bottle?
The kit didn't know I had a fastferment.

Ideally you want to bottle clear beer. So, you need to make sure that you've removed as much sediment as possible. It only takes a tiny amount of yeast to carbonate.

Once the sediment is removed, you can dissolve the sugar in a small amount of water, boil it briefly, then add it to the beer (while hot is just fine). Stir that and bottle immediately. Having the sugar already dissolved in water will let it disperse more evenly and prevent foaming when mixing it.