I think that there should be a video showing how to use L.a.b. colour to rescue flat files. I used Photoshop for years for this purpose now I am getting to grips with the different process in Affinity. The present videos do not do justice to this powerful tool. I have attached a before and after edit which only took a couple of minutes using Curves in L.a.b. For your info they are in the South Australian outback. There is much more to L.a.b. and it is the main reason that I chose Affinity when I gave up Photoshop
Eric