Please help me locate my iPhone 7

Sorry to hear that you have lost your iPhone 7. 

To locate it in the Find My [Device] app, you must have activated the Find My app BEFORE the iPhone 7 was lost. Here is some information on that app If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support.

Note that your lost iPhone must be able to make the connection to the internet via Wi-Fi or cellular connection so that it can mark its location and broadcast it.

Good Luck.

Axel F.

Your iPhone must also be on, and have charge.