How To Plant Grass Seed

I Bought A New House And Had Sod Laid In The Whole Yard. I Had To Leave The Weekend That They Laid It And Everyone Knows That When Sod Is New, You Have To Water It For At Least Three Days Pretty Much Non-stop. Well I Couldn't Be There For The Weekend And I Came Back 2 Days Later And My Grass Was Cooked. I Have Been Spending So Much Time On Trying To Get It Back To How It Used To Be But There Are Still A Few Spots That I Don't Think Will Come Back So I Wanted To Plant Seed On Them. Do I Need To Tear Up The Old Sod Or Can I Put The Seed On Top Of The Sod And Water It? Any Suggestions?