So you scoop out your Betta with his old water, keep him aside for now. You go and refill your tank with new water from tap, use your conditioner.
If you filled the cup up all the way with water, pour out half of the water at least, you can cover the cup with your hand so that he doesn't jump out.
You don't necessarily have to float him. So now he's still in his cup with the old water from before, only filled half way now. Now you have new water in your tank, you used conditioner on it and that's all set. Now you take a Tablespoon of that new tank water and put it into his cup. So that now it mixes with his old water and he has new water. Keep putting 2-3 Tablespoons in every 10-15 minutes to his cup so that eventually it will fill up.
So because you are mixing old water with new water it makes it easier for him to get used to the new water. One the cup is filled up he's ready to go into the tank because he's acclimated to the tap water. Make sense?
What kind of Betta food is it? Sorry, just want to make sure you're on the right track is all
not all foods are created equal. Look at the first three ingredients and tell me what they are. The things you want to watch out for are called Fillers, these consist of Wheats, Corns and other Soybean products and if those are in the first three ingredients the food isn't very good. The more fillers are in the first three ingredients the worse it is.
I highly recommend Omega One Betta Buffet pellets as they have no fillers in the first three ingredients and New Life Spectrum betta pellets or Small Fish formula which only has one filler in the first three but is a really good food