As with any photo restoration, there are many ways to go about the problem. You could try to restore one of the patterns on the wallpaper and try to clone it over the wall to make the pattern repeat. It might be that it is so damaged you need to replace the paper altogether.
This technique can be used with any shapes or patterns or texture to make a wallpaper.
1- Make a new image with 500 x 500 pixels
2- For this example ill use a preset brush. Select the brush tool from the Photoshop tools pallet.
Choose one, a leaf will do.
Now select the tiny paint pot to the right of the size slider on top of the preset brush pallet and you will see a whole new set of controls. These control the shape dynamics of the brush. I won’t go into these in too much detail but you can just copy the settings from the next screen grab. Dynamics allow you to change the way the shapes are thrown down on the page, the angle, colour, randomness, pressure, spacing, a whole bunch of things. You probably never thought you would even use these controls in photo restoration, did you?
Once selected choose two colours to paint with and paint on the canvas a few times. You could just as easily skip this step and use an image for the middle of the design.
Then select Filter/ Other/ Offset from the filter drop-down menu. Select +250 on both sliders and tick the checkbox wrap around.
The reason for this is we can add another pattern in the centre to create a convincing repeating wallpaper. Paint in the middle with some other colours, or you could paste an image in the middle.
Now create a new canvas say 4000 x 3000 Now from the top menus select Edit – Define Pattern, save as pattern name you prefer. Then Edit / fill / pattern and select your pattern and fill your background or new image with that pattern
Once you have as much of a repeated wallpaper as you like, make sure the layer is selected. From the top drop-down menus select Edit/Transform. from here you can Warp, scale, Skew and add Perspective to the image you have created.
Using your imagination and textures from the photo or perhaps even wallpaper samples found on the net, you could produce a very convincing wallpaper to replace the existing one in your photo restoration.