1- Open Affinity Designer.
2- Upload your design or image.
3- In the top left of your screen select the Pixel Persona, this will bring up a new toolbar on the left of your screen.
4- Click on the Selection tool.
5- Select the area that you want to edit. Click on the Refine tool.
6- The area you do not want to edit will be highlighted in red.
7- You can use the selection tool to refine your selection even further. When you are happy select apply.
8- You can now adjust your selection. Click on the adjustment icon in the layers panel. Select the adjustment you would like to do.
9- I selected HSL s o I can affect the sky and make it brighter in this image. As you can see the adjustment only affect the selected area and not the jetty in the image.