You can use different methods to cover the gap above your dishwasher.

The quickest and easiest way is using wood to fill the space.

You can do this by following these steps:

Measure The Gap Cut Wood

Measure the area with a measuring tape. To do this, place the tape next to the space, and it will indicate the distance between the two objects.

Cut & Paint Wood

Cut the wood that will be able to fill the space between the dishwasher and the countertop.

Add a Bracket and Fasten The Wood Panel

Locate the final one in the exact middle of the dishwasher. Next, add the wood panels on the bracket.

Bind The Pieces of Wood

Use putty along the wood to cover up all of the joints. There should be no gaps or openings visible between the wood panels.