Restoring Files from an iMac that had a reset.

Basically you cannot. You may have some data files stored in iCloud however if you never turned on iCloud then your all of stuff is gone. There are data recovery services available however be prepared to spend north of 5 figures to recover your data.

This is EXACTLY why a strong backup plan is not something you should do it's something that MUST be done.

In your case the fire has already burned down the barn and you are asking about the horses that were inside.

Sorry to tell you exactly what you did not want to hear, many experienced users have learned the hard way too why current backups are critical so don't feel alone.