The Brush Tool lets you blend the image with a source photo in a specific area instead of the whole image. To do this:

1. Adjust the Opacity on the left panel. If you want to completely replace an area with the source photo, set the Opacity to its maximum of 100.

2. Click and drag on the image to blend the source photo with the area you select.

If you wish to apply different blending adjustments to another part of the image, then click on New Selection.

When you close this window, you will be leaving selective adjustment mode, and further blending adjustments will be applied to the whole image.