What if I don’t have a computer to do so

you should probably provide more details.. such as what you've tried and whether you're getting an error.

you generally don't need a computer to update your iPhone.

Here are some links/videos that may help

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

Updating iOS: common issues and solutions - Apple Community

If you don't have a friend with a computer who will help you, make an appointment at an Apple Store for assistance.