Noob question: fill a white space by blending the colors around it

Problem is, I don’t really know what to call the operation I need to do. The attachment shows a white space surrounded on three sides by different shades and texture of blue.

Is there a tool or process whereby I can fill that white space with gradients of the blues taken from the edges? I assume I would need to start with a layer to match the white space. If there is a tutorial I missed in going through the docs, I’d be glad to use it!

The image is a .png screenshot from some aerial orthoimagery.

M1 Big Sur
Mac mini
Acorn 7.1

Screen Shot 2021-09-24 at 16.58.20

What you want is sometimes referred to as “inpainting”, though I’m not sure your example would suit that process very well. (Acorn doesn’t support inpainting at any rate).

I would suggest using the clone tool, and then using the smudge brush to blend the colors.