Ok....the truck will not start. where do I have it flashed to my calibration?

Ok great.
I thought all of the Im two horny chips all were two position switches?

Will It do any damage if my truck has already been flashed? or will it simply over ride the flash?

I have a 2000 f350 7.3 L and I am not sure if it has been reflashed before but it runs realy good and this leads me to believe that maybe it has....and my buddy just gave me the I'm two horny chip out of his (early model) 99 f350.

It did not come with a switch to go back and forth between the ...