A person sold you a non-started hatchling? Wow..

What do you have the snake housed in?

If the snake has never fed, wait until dark, make the room dark and offer a LIVE hopper mouse. Wait 30 minutes to an hour, do not disturb the snake, and then remove the mouse. If the snake doesn't eat, wait a week and try again.

Babies are extremely hard to get started on frozen, if not impossible.

Hopefully you have the snake in a 6qt shoebox tub with a dark hide.