Lost iphone

You don't, sorry.

These are the only steps you can perform in such a situation:--> If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support and/or:--> Use the Find My app to locate a missing device or item - Apple Support

Regards

Giulio

Unfortunately the only way that you will be able search for the iPhone is using the old fashioned method of looking for it the same way that you would look for your wallet or car keys if they are lost. Depending on the area where the phone was lost, you might want to post some notices and ask about things at any stores or restaurants in the vicinity.

Hopefully, you had a passcode set up on the phone, which will lock out anyone who might try to log on