You’ll need to apply moss killer to kill the moss, then do a soil pH test to see how much lime to apply to get the soil back to neutral. This acid soil is the reason the moss is thriving and the grass is dying. You can apply lime and grass seed to help the grass reclaim the area. Do another pH test in the fall to see if the lime you applied did the job. HERE A LINK to a post about how to do a PH test.