Thanks for your assistance.

My Font yard is: 1578sqft
My Back Yard is: 1450sqft

I am only growing lawn.

I figured all I had to do was boost the nitrogen, but do stores sell
only nitrogen? I thought most fertilizers had all kinds of stuff in it
like potassium, phosphorus, etc.

Lastly, since my pH is 7.9 and St. Augustine is supposed to be around
7.0, do I need to bring it down to around 6.5? I currently am at 7.9ph
and I wonder if this is a big deal or can I ignore this?