How can I make my iPhone to be on iOS 13

You can't, it will only update to the latest iOS which for an iPhone 11 is iOS version 16.4.1(a)

Update your iPhone, iPad, or iPod touch

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.7

• If you have an iPhone 6S through 7, you can update to 15.7.5

• If you have an iPhone 8 or higher, you can update to 16.4.1(a)

Go to Settings > General > Software Update.

This link will show you how to update your iPhone, iPad, or iPod touch using WiFi -

Update your iPhone or iPad - Apple Support Update your iPhone or iPad - Apple Support

This link will show you how to update using your computer -

Update iOS on iPhone - Apple Support Update iOS on iPhone - Apple Support