Apple Races to Tweak Software Ahead of Looming US Watch Ban (2)

Apple Inc., just days away from a US ban of its smartwatches, is plotting a rescue mission for the $17 billion business that includes software fixes and other potential workarounds.

Engineers at the company are racing to make changes to algorithms on the device that measure a user’s blood oxygen level — a feature that Masimo Corp. has argued infringes its patents. They’re adjusting how the technology determines oxygen saturation and presents the data to customers, according to people familiar with the work.

It’s a high-stakes engineering effort unlike any Apple has undertaken before. Though the iPhone maker’s products ...