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In the upper-left of the toolbar, there are some marque tools. You know, rectangle and circle and stuff. One of those is horizontal single pixel select. Choose that one.

Drag it out over your target.

ctrl + j

ctrl + t

Grab the top and drag up. (Assuming you are going up. Could very well be down; or to the left or right, in which case use the vertical single pixel select).

Then it's just a matter of layers, layer order, and/or layer masking.

In the future, please use a  more descriptive subject title. It makes it easier for us. You know, help us help you.