I'm talking to the builder now and they will fix the sprinkler, but the lawn isn't covered under warranty. (which I understand, I should've checked it to begin with but that's my own fault)

I've scoured all over trying to find out what I can do now and the only response on any post is "how have you been watering it?" and "here's how to check it"

My question is simple:

My new lawn has not had enough water for about a month and is more yellow than green, what can I do now?

The question that comes to mind for me, is which part of the State are you in? If you've had cooler temperatures lately, that can stunt St. Augustine enough to discolor it. Lack of water shows up initially with wilting, rather than discoloration. This is easy to see in St. Augustine, because the leaves will fold up tightly right at the mid-rib, as the grass tries to increase the transpirational pull on the roots. If it didn't do this prior to losing color, then it's either reacting to winter temperatures, or there is a nutrient deficiency. Either way, a good potassium fertilizer with minor nutrients will help your cause.

One last note, make sure not to use fertilizer blends that include weed killers. St. Augustine is very sensitive to a group of herbicides, phenoxy acids, that are frequently found in weed and feed products. Look for active ingredients like 2-4-d or mecoprop (mcp) and avoid these.