You can first select the part in the middle white, copy and coexist a layer (you can use the magic wand+lasso tool to select), then use the magnifying tool to enlarge the new layer to the size of the outer frame, and then choose to delete the outer burr on the old layer in reverse.

Or use the new layer to reduce it to the internal blue size, then copy the new layer from the old layer, divide the latest layer into two layers, and finally gradient the two layers.