Cut out a patch of wallpaper that you are going to use to replace the damaged section. Patterns on the patch and the original wallpaper must be identical or otherwise the patch you use will look out of place and ugly. Cut out a patch of new wallpaper using a utility knife. Make sure its size is a few inches bigger than the damaged wallpaper section.
Now it comes to applying the wallpaper patch. There are two possible ways to do that. Either you can apply a uniform layer of wallpaper paste to the back of the patch and then apply it to the damaged section, or you can apply some adhesive material to the wall, wipe the back of the patch with a damp cotton ball and then make it stick to the damaged area. Choose either option that you think is convenient for you.
Place the patch on the damaged area and firmly press it against the wall. Give it time to set properly. Three to five minutes will be a reasonable duration of time. Since the patch was a few inches bigger than the damaged area, you need to get rid of the excess wallpaper. Use a utility knife and a straightedge for the job. When you get rid of the excess wallpaper, your work is almost done.
Carefully remove the correct sized patch from the wall.
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When you were resizing the replacement patch, you would have left cuts of the same dimensions on the original wallpaper as well. Find those cuts and use them as a reference to remove the damaged section of the original wallpaper. When you are done, the bare wall section and patch you are going to use as a replacement will be identical in dimensions.
Finally, you need to paste the replacement patch again to cover the section of bare wall. They should be an exact match because the old wallpaper and the replacement patch were cut simultaneously.
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