Stolen phone

If it is turned off you cannot.

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

"Don't see your device? You might not have Find My [device] turned on. If your device is powered off, the battery has run out, or more than 24 hours has passed since its last location was sent to Apple, you also can't see your device's location. Learn how you can still protect your information."

Click on the link to find general information about what to do "If your iPhone, iPad, or iPod touch is lost or stolen" --> https://support.apple.com/HT201472

Make a police report.

Anything that could be done with remote technology will require the device be powered on, and connected to the internet. An iPhone that is powered off is an inert hunk of plastic and metal.