There are a few ways to find the radio code:
First, check in the owner's manual pouch (if you have one) if there's a credit card sized card with the radio code printed on it.
Otherwise, normally one would go to the original selling dealer where the car was bought and they might have it in theri computer system in service. If notm then in some cases, the dealer can pull out the radio and get the code off the radio serial number in the back of the radio unit.
Since you have a Daewoo, and chances are the dealer does not exist anymore, that might be hard to do.
I'd recommend getting an aftermarket unit as they're inexpensive nowadays, if you have no way of finding the radio code.