Hi there. It's early days and you're doing well to get a nitrite spike so early. The bacterial bloom, presuming it to be milky white, will clear in time and needs no treatment.
When cycling I normally only water change to keep the nitrite and nitrate reading about mid scale on the colour charts, if it's off the chart then you can't tell if it's rising or going lower. If your reading are not off the chart then I'd leave it alone, apart from maintaining a decent ammonia level to feed the bacteria. I keep my tanks at 4ppm ammonia whilst cycling and at 2ppm when cycled but awaiting fish, just to keep it ticking over.
Obviously a huge water change is required before the fish arrive so that the nitrates are well below 20ppm. Then you're good to go. Enjoy.
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