You don't have a book on VB.NET ? Writing loops is the most basic thing I can thing of after 'hello world'. I am happy to help, but it won't help you in the long run if you can't do basic research and/or have no resources. I even gave you the key words to type in to google.
Dim b as Byte
for each b in myAscii
that gives you a loop, inside which you can add each byte to a string, preferably using a stringbuilder.