If most of your lawn is in pretty good shape, I would just rake up these spots with a thatching rake to the point where you have almost pure dirt. You might even just scoop out the bunch grass with a regular shovel and then rake the dirt around it to fill it back in and loosen it up. Mix some new seed in with the dirt and spread evenly.

If you spray roundup, you will have to wait for it to die and then you will still have rotting blades in place for a month or so. If you rake these spots out now and seed, you'll have plenty of time for the new grass to get established before the oncoming winter.

If it's hard fescue, it comes out pretty easy.
I'd hand pull and reseed