You need to rototill the ground to a depth of 2 to 4 inches.

How to level backyard soil. Dethatch your lawn [as needed]. Use these 8 steps for how to level a yard to ensure great results. Common tools are only needed:

Dig up the grass in the sunken area of the lawn. After rototilling, build the leveler by using 3. For you to fill a hollow, you need a garden.

Mow the lawn step 2: Use leveling sand to fix uneven. To level bumps in your lawns, dig enough soil until you get the same level with the surrounding area.

This area does not need to be perfectly square or rectangular unless you are planning on using sod instead of simply replanting your grass. Opt for two parts pure sand, two parts of topsoil, and one part of compost. Dethatch your lawn [as needed].

Examine the condition of the lawn step 3: I've added an image below to illustrate. I use metal stakes but wooden stakes will work just fine.

Mow your lawn step 2: This is a short video on how to get your ground level in order to install seed or sod. Dethatch your lawn [as needed] step 3: