That's hard to do. If it's still fermenting, you could try sticking it in a fridge until it's totally clear, and then racking it onto some campden and sorbate to make sure fermentation doesn't recur. that's tough to do though- because yeast don't stop just because we want them to. Stopping an active fermentation is like stopping a freight train.
If the yeast falls out, and the wine clears, though, sometimes you can encourage the yeast to not start up again by making sure there are no lees (lots of yeast in the lees) and the wine is completely clear before attempting to stabilize.
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