Learn to Extract in Photoshop

Step 5 –>  Fix the Imperfect selection

Hold down the left click of your mouse and drag it over the unselected region as shown in the screenshot below.

Now select the non-selected area that needs to be included by repeating the step given above. Try to be careful, however if you aren’t able to do it perfectly, it won’t matter since we would be using the refine edge tool to give our extraction process perfection.