How to remotely lock iPhone 7

kumerica wrote:

I want to lock my stolen iPhone 7 with serial number

There is no means to lock an iPhone by serial number, IMEI, or anything other than Find My.

Here is what to do: If your iPhone or iPad is lost or stolen - Apple Support

If you turned off Find My, there is no means to enable or re-enable that remotely.

Please follow these instructions:

If your iPhone or iPad is lost or stolen - Apple Support

I want to lock my stolen iPhone 7 with serial number

This is not possible using the serial number or the IMEI. Find My is the only way to lock the phone.