Apple finished the trading day Friday up 4.3 percent, paring losses from its worst day since 2013. The stock fell nearly 10 percent Thursday after Apple cut its forecast for its fiscal first quarter, blaming weak iPhone sales and a slowing Chinese economy. Apple was still down 5.1 percent for the week.

Apple lost tens of billions of dollars in market value Thursday, ending the trading day at $142.19 per share, its lowest since July 2017. In just three months, the stock has shed $452 billion in market capitalization — a loss that outsizes Facebook's total market value. From its 52-week high of $233.47 per share on Oct. 3, Apple shares have fallen by 39.1 percent as of Thursday's close. Its market value is now around $674 billion.

Apple suppliers like Corning, Lumentum and Qorvo were also positive on Friday, after taking a hit on Thursday.

Investors have feared for many months that iPhone sales were not as rapid as they used to be, and Apple's letter to investors Wednesday confirmed those fears. In an interview with CNBC's Josh Lipton, CEO Tim Cook said his plan for turning sales around includes pushing Apple's trade-in program to minimize the cost of a new iPhone to consumers, ramping up payment plans and hand-holding customers through the process of upgrading their phones.

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Watch: CNBC's full interview with Apple CEO Tim Cook