Two options, easiest is to cut it out with a knife or other similar tool, cut around the border and maybe crosswise, the roots are a few inches in so with a spade it should be easy to pull out. This is how I handle the problem, as I get a few tall fescue plants in the lawn every so often.

The other option is a grass based herbicide you can purchase at any store that sells that type of product (menards, hardware stores etc). In the evening, during cooler periods with low winds, make sure to spray just that grass and not the lawn...since they will both react negatively. Doesn't hurt to have watered the lawn earlier in the day so that the grass is not drought stressed and more open to accepting the chemicals used on it, and it should not have been mowed recently so that there is lots of grass surface area to accept these chemicals. 

Once the invasive grass is dead, wait until mid to late August to start any new grass seed. Fall is a great time for getting lawn established, once the heat and drought of summer has passed.

Good luck!