Can I turn on my location remotely on my stolen iPhone?

If you are asking if you can turn on the Find My option on your phone remotely, to allow the phone to display its location on a map.......the answer would be "no".

This option must be turned on......before.....the phone is lost.

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

No, it has to be turned on before the phone is missing.

It it not possible to change the IMEI on an iPhone.......unless.......you open up the phone and change the logic board.

No thief is going to bother with this type of complexity, they just want to sell the phone as quickly as possible.

Next time, turn on the Find My option on your phone and leave it on.