Filling in 'dips' in lawn
 

Greetings -

I have a couple of 'dips' in my lawn - areas where several square feet are
several inches below the rest of the lawn. Grass is growing there
currently. What is the best way to go about filling these holes, so they
are up to grade with the rest of the lawn? I thought about just filling it
with topsoil, but do I need to remove the grass there first? Should I till
it up first? Should I tamp the topsoil down, or just leave it in there
loose, then reseed?

Thanks for any help!

=Scott L.