In order to get brown patch under control it is best to take both preventative measures  through cultural control ( see below) and curative treatment with fungicide. 

Although the fungus is not active right now, it survives the winter in a dormant state inside the dead grass tissue and in the soil.

You will want to treat the area with fungicide in the spring prior to reseeding. Treating now will not be effective. 

This link has everything you want to know about control of brown patch including recommended fungicides. It also discusses steps to take for cultural control and prevention. https://www.turffiles.ncsu.edu/diseases-in-turf/brown-patch-in-turf/#:~:text=Avoiding%20prolonged%20periods%20of%20leaf,wetness%2C%20do%20not%20irrigate%20daily.

You will want to wait several days after fungicide treatment before overseeding.

Growing turf grass in our area is always a challenge since we are in a transition zone. Thus, while both warm and cool season grasses grow here, the climate is not optimum for either. 

The trick with fescue is to follow the maintenance calendar –https://content.ces.ncsu.edu/tall-fescue-lawn-maintenance-calendar – taking care not to overfertilize or fertilize at the wrong time and to follow proper watering recommendations so that the grass has time to dry out before evening and to be sure not to overwater. Water deeply but infrequently, so that the grass gets about 1 to 1.5 inches of water per week.

Also avoid cutting it too short. The recommended height is about 3.5 inches.

While you can overseed in the spring, September is the best time for fescue renovation.

If you are interested in a definitive diagnosis you can submit a sample to the Turf Diagnostics Lab at NC State University. Instructions on doing so are here: https://turfpathology.ces.ncsu.edu/diagnostic-lab/how-to-submit-a-sample/ There is a modest cost for analysis of $30, or if submitted via an extension agent $20.