What steps do I need to take to find my iPhone?

my iphone 11 was stolen from my car while it was in the pound and i have no clue what my apple id for that phone was i previously had a iphone 7 so when i type in my information for the forgot id it only takes me back to the iphone 7 its like i dont even have the iphone 11 i have my box and original packaging for my iphone 11 with the serial number on it what steps do i need to take to find my phone

[Re-Titled by Moderator]