SINGAPORE—Factories have reopened and manufacturing is steadily choosing up in main manufacturing areas of Southeast Asia as Covid-19 instances have dropped in current weeks, easing a few of the supply-chain constraints that firms blame for misplaced gross sales.

Apple Inc. grew to become the most recent firm to point to the situation in Southeast Asia as a bottleneck , saying on Thursday that pandemic disruptions had contributed to a $6 billion hit to potential income.…