Stolen iPhone - What to do?

Hello! I just bought a brand new iphone XS Max and it was stolen from me last night. The iphone was a month old and I had forgotten to enable Find my phone for this phone.

Is it possible to turn the phone to Lost Mode without using Find my phone or somehow turn Find my phone on remotely. It seems that the phone was turned off right away, since there was only a fifteem minute window in which the phone had been taken from my purse. We called it right away and my battery had not been low, so there is no way it died.

Please help me, what can I do?

Thanks in advance.

Hilla