Hmmm, not exactly sure what you're asking, but I will answer the way I think you're answering. Typically on down tube shifters you push the lever all the way forward to the front of the bike, insert cable, run through housing to the derailleur, which would necessarily be in it's relaxed state. When you shift, you are pulling the shift lever back toward you (toward back of the bike), thus tightening the cable & causing the derailleur to move.

So, push both shift levers all the way forward & adjust from there. Photos would help too. Are you shifters brazed onto the downtube or on a clamp?