If you already have a byte array then you will need to know what type of encoding was used to make it into that byte array.
For example, if the byte array was created like this:
byte bytes = Encoding.ASCII.GetBytes(someString);
You will need to turn it back into a string like this:
string someString = Encoding.ASCII.GetString(bytes);
If you can find in the code you inherited, the encoding used to create the byte array then you should be set.