The Trade Act didn’t delegate unilateral tariff authority to the President. It allows some action to be taken to counteract unfair trade practices (which must be specified and specifically targeted), but that’s not what Trump is doing. A 50% tariff on India or Brazil has nothing to do with unfair trade practices, nor do these tariffs on alcohol, nor do the blanket tariffs he’s imposed elsewhere.
Trump’s arguments so far before the court have been that the mere existence of trade deficits are indicative of unfair trade practices, but that’s farcical on its face. Fortunately the courts have so far ruled against him on tariffs, and hopefully the federal circuit and SCOTUS will as well.