How do I patch up this plaster?

[teaandakitkat]

I stripped wallpaper off today and this patch of plaster has come off. It's like the top layer, maybe 1cm thick, no more than that.
We are going to paper the walls and it's in a corner than will always be covered by a bed so not very obvious. But I still want it to look ok.
Do I fill it with polyfilla? Or something else? It's maybe 10cm by 20cm.
Please don't tell me I need a plasterer, they are such a hard trade to find round our way and our new carpet is coming in 2 weeks.
What a nuisance, the rest of the walls are totally fine.

[Pumperthepumper]

Pollyfilla. Wait for it to dry then rub sandpaper over it until it’s smooth 👍

[Ragusa]

Yeah you can fill that. It's going to be hard to get smooth. My suggestion is slightly overlap it with the remaining plaster and overfill it a bit. Polyfilla usually sinks a bit as it dries.

[PigletJohn]

jointing plaster, as used to fill the gaps between pieces of plasterboard. It is relatively inexpensive and better than filler.

www.wickes.co.uk/search?text=joint%20plaster

A plasterers trowl or wide knife
www.wickes.co.uk/Marshalltown-MDR390-Flexible-Jointing-Knife-M-pact-End-4in/p/117902
will help you get it flat. Rule off the first coat by rubbing a long piece of wood in a sawing motion across it, pressing on the flat wall at both sides, then again holding it vertically. This will remove any high spots and display any hollows, which you can then fill with what you've sawed off. Never leave a patch higher than the surrounding wall, the effort to abrade away the lumps is much greater once set.

When the first coat is hard, apply your thin skim of finish with the widest trowel you can handle. Yours looks too big to use a knife. Press very hard. If you have to remove any, use a wide metal scraper, preferably while it is cheesy. not sandpaper.

You can polish the final surface after first set with your plasterers trowel, after spraying it with water. You don't want a glassy polish or paint won't stick.

Mix small amounts that you will use up before it sets.