We recently installed a laminate floor in living and dining room. The subfloor
Was in good shape, seemed to be quite level throughout. However, now
That the floor is installed there are spots that are defininately lower and
"soft". Any suggestions to fix this short of removing the flooring and
Starting over?

Sorry but "removing the flooring and
starting over?? " is where you need to go. There is no way of injecting anything into the low spots. You could have used a poured floor leveling compound before installation had you known it was not flat