How to blend a mottled background (retouching an old photo)

[frank99]

I am restoring an old photo where the background is mottled and uneven (partly the result of my attempt to cover up a torn section of the background). How do I blend the background together so it looks even and does not mottled? I'm not sure what tool and what settings to use. The area in question is to the right of the subject's head. I think this is a question about how to blend an uneven background, but I am unsure how to do it. I have created  separate pixel layer to smooth out the background, but what's my next step (or steps)? I think it's pretty basic, but I am new to Affinity Photo.

area in question is the background to the right of the subject's head.

[firstdefence]

Welcome to the forum @frank99

You had Hardness set too high so you are seeing defined edges, if you can go back and do it again use a softer brush setting. You can change the Hardness of a brush from the context menu just above the workspace or in the brush settings by clicking on more... on the same context menu.

When repairing it usually takes a combination of tools. Without seeing the unedited image it's hard to say what tools would be most effective. To correct this mistake try the inpainting tool (J), work from the top of the brushmarks  downward, then do the same thing but going upwards, you can also deal with the slight creases on the left with the inpainting tool. Make small to medium selections and you should end up with something like this...

[carl123]

An alternative method for a blank damaged background is just to create a new background from scratch

Separate the background to a new layer
Sample dark brown colour from top of background
Sample light brown colour from bottom of background
Add a gradient using those colours to the new layer
Add noise to layer as required (to age it a little or a lot)

Quick example attached, would need to spend more time refining the separation of the background layer in the first step
 

 

[Hilltop]

You might want to check out some YouTube Affinity Photo tutorials to not only remove tears and other blemishes but also to improve contrast and such: 

https://www.google.com/search?q=restore+old+photos+in+affinity+youtube&oq=restore+old+photos+in+affinity+youtube&aqs=chrome..69i57j33i160.10936j0j7&sourceid=chrome&ie=UTF-8