How do I update my iPhone 6 to ios14 ? Please I can lose my job over this

you can't. If you need to run iOS newer than 12, you'll need a newer iPhone model

iPhone models compatible with iOS 15.5 - Apple Support

Your iPhone 6+ is not capable of using any iOS other than iOS 12.5.5. Your only option is to get a newer iPhone.

You can't . Your iPhone 6+ only supports up to iOS 12.5.5

While it's been made clear you cannot update such an old iPhone, why would you lose your job over not being to update an iPhone?

Then his employer needs to provide a device which can run that app if it's required to do his job.

Perhaps his job requires him to use an App that needs a version of iOS after 12.5.5?