I got an iPhone 6s so my problem are when it comes to update software it’s not working what is the course

The iPhone 6s is capable of running the current version of ios, 15.6.

If your phone is running 12.5.5, it is NOT a 6s. It is a 6.

These are the iOS options based on iPhone Model --> You need to Identify your iPhone model - Apple Support

• iOS 15.6 —> 6S / 6S Plus, SE (1st Gen and 2nd Gen), 7 / 7 Plus, 8 / 8 Plus, X, XR, XS /XS Max, 11,11 Pro /11 Pro Max, iPhone 12, 12 Mini, 12 Pro, 12 Pro max, iPhone 13, 13 Mini, 13 Pro, 13 Pro Max
• iOS 12.5.5 —> Final release supported on iPhone 5S, iPhone 6/6 Plus, 

Learn how to--> Update your iPhone, iPad, or iPod touch - Apple Support

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