You can do this pretty easily, because I've done it.
I had my driveway/lanai/patio painted and sealed in 2012 on a new home. Normal sealer lasts about 4 years with a double coating of sealer. My initial contractor only did a single coat, so in 2015, I bought some sealer at Lowes, got a long-handle roller and applied it - two coats this time. I think it looks great and has worn well. I can tell that I'll have to do it again, this year or next. You can do this for less than 1/10th of what you'd be charged, and do a better job. Good luck.
https://www.lowes.com/pd/H-C-Concret...-fl-oz/3390426