Can I rewind and record live tv program that my DVR saved?

I was able to watch and record the last half hour of a 1 hour show.. my dvr was able to save first half hour while I was away and the tv was on so i rewinded and didnt miss anything, but i wanna record the first half hour as well.. Can i do that and if so how do i do it? It wont do it if i just push record button from the beginning..