how to erase my iphone using a serial number

There’s no such means; not by serial number. That’d be massively abused. As was stated earlier.

The IMEI can be blocked, but that’s not world-wide.

More reading on what is available:

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

Use Lost Mode in Find My iPhone on iCloud.com - Apple Support

You cannot do that.

If you could, it would mean that if you happened to see my iPhone's serial number, you would be able to erase it. I would not be very happy if that happened.