How do you reset the Radio after no power in a 2008 Honda fit

https://www.youtube.com/watch?v=6R72mm75LaM tells you how to extract the radio serial number.

THEN go to the genuine Honda website https://radio-navicode.honda.com

Which will need the VIN number and the radio serial number to give you the code. IT'S FREE.

You sure you looked through any booklets in the car? It'd be in one inside the front cover or front few pages.