How can I locate my stolen iPhone SE without Find My?

I'm sorry, but you must set up Find My on the iPhone SE......before......it is lost or stolen.

The only thing that you can do now is retrace your steps and check in shops and restaurants that you have visited to see if someone found the phone and turned it in to the manager.

If Find My was not enabled, you cannot track the phone.

Since the phone was stolen, the chances of recovering it are slim and none. With Find My turned off, the thief could reset your phone and "make your phone their own." They may already have done so.

You could ask your carrier to blacklist the phone. If they do, no carrier who honors the blacklist will provide cellular voice, message, or data service to the phone again. This won't make the phone a complete "brick", but will "brick" its ability to act as a phone.

Hopefully

• Your phone was passcode-locked, with a passcode the thief did not know and could not easily guess. This would keep the thief from ransacking your data.
• You were making iCloud backups of the phone or were using synchronization features like iCloud Photos, so there is data that you can restore to a replacement phone.

Read this support article to learn what you can do if Find My iPhone or Find My iPad isn't enabled on your missing device --> Find your lost iPhone or iPad - Apple Support

Use Find My to locate your lost Apple device or AirTag - Apple Support

If you did not set up Find My on the stolen device before it was stolen you will not be able to use it to locate that iPhone.