Need pictures.

"Big crater" sounds like they removed the mulch ("sawdust") for you. There is still probably some there mixed with soil, so rake and shovel the perimeter and pockets and move it to the center fill. Not only will remaining mulch continue to compost, but the soil fill will settle. So it may mean a matter of retopping periodically for a couple years.

For future stumps, dig the soil away from roots that extend out from the trunk. At most a service might hit a couple large visible ones near the trunk base, but if you want more removed you'd have to expose them and ask for it ahead of time.

Fill with topsoil, add compost and fertilizer. Then buy a bag of 50 assorted daffodils and plant them before the ground freezes. They will bloom in spring. You can move them after they bloom or when they go dormant in late summer. Refill the crater with new topsoil and seed with grass if you prefer grass to bulbs.

Boston - Cambridge · More Info

Speaking from experience here: if there is visible sawdust or other tree debris, remove all that is feasible. I had a tree stump ground out and the tree guy told me that the sawdust would decompose quickly and make the soil conducive to growing grass almost immediately. He LIED.

We lived there 7 more years and I never was able to get grass to grow there. And the spot kept sinking.

Pics would be a huge help but I agree the stump will continue to rot for years so IMO grass not an ideal choice but who knows what to suggest with no context.