My other iPhone says an update is required to activate what am I supposed to do

Hi there,

It seems like your iPhone needs to be updated through your computer.

If you use a Windows computer, you'll need to install iTunes on your computer. Then, you can follow this guide: Update software on iPhone, iPad, or iPod touch in iTunes on PC - Apple Support

If you use a mac, you can follow this guide: Update software on your iPhone, iPad, or iPod touch - Apple Support

I hope that helps

What model iPhone is it?