I have some patches on my lawn to re-seed. They turned from green to white,
and the grass is dead.

How much of that dead white grass do I need to remove? Can I loosen up the
dirt, drop seed, top soil, and starter fertilizer or do I need to dig into
all the dead grass and remove it ?

My grass is fescue (Marathon) and I live in the foothills of Los Angeles.

Thanks.