How can i find my iphone even if it does not have service

Click on this link to read how to "Use the Find My app to locate a lost or stolen device" --> https://support.apple.com/HT210515

The chances of locating a device depend upon which features you selected in:

Set up Find My on your iPhone, Mac, and other devices - https://support.apple.com/HT210400#enablefindmy

Note the utility of Bluetooth location in the article, and as mentioned by Lawrence Finch. If your device is not connected to Wi-Fi that is the only way Apple's Find My feature can locate it. That is the only finding service Apple offers, otherwise you have to resort to the ways you would use to locate any lost item such as a set of keys.

With your eyes. If it has no Internet connection it cannot be found electronically. The one possible exception is if Bluetooth is enabled there’s a slight chance that a passing stranger with an iPhone might pick it up with bluetooth and report it.

You can’t track it without it being powered on and connected to the internet.