I want to update my iPhone to 13.5 please

There is no model of iPhone capable of updating to iOS 13.5. To update to the most recent, compatible version, please see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

If you're referring to an iPhone 6s or newer, use a computer or the Software Update function in Settings to install 15.7.2 or 16.2.

If you're referring to en earlier unit or trying to install exactly 13.5, you can't.

(231102)