IOS 14.4.2 not installing for my iphone 6s

Connect it to your computer and update it there.

Update your iPhone, iPad, or iPod touch - Apple Support

Maybe you do not have an iPhone 6s?

Tell us what you see in Settings > General > About > Model Name > ?

What version are you currently running?

If it is a PC you use the current version of iTunes. Click on the blue link in my post above yours for instructions.