Fix brown patches of grass to look greener

A few different approaches might work ... such as use the Lumetri HSL keyer to select the area, then in the controls below the key-creation controls, modify the color/brightness whatever to be more to taste.

Or create an adjustment layer, put a color-matte on it with a lowered opacity along with (through) a mask for that area, and work with it until it gives the improvement in color you want. That might work.

Or use the first, a Lumetri effect but applied a couple tracks above the 'main' video, through a mask on the layer below it.

Neil