How to shoot a full-length portrait with a pure white background

First of all, you need to completely brighten the background, hit the background with two lights, one left and one right, and adjust the lighting index to the highest. Then turn off some exposure options in your camera, such as Nikon's "Dynamic D-LIGHTING" and Canon's "Automatic Brightness Optimization" and "Highlight Tone Priority". So the background can be completely white. If the edge of the picture is black, add some soft cloth or something in front of the background light to beat the light evenly.