Gloss Paint on Plaster Walls

sand down and apply water based under coat

Sanding will remove the gloss from the walls and provide a "tooth" for new paint to adhere to the old. ... Use a medium grit sandpaper (about 150). ... Wash the walls with a TSP (trisodium phosphate) and water to remove all the sanding dust, and let the wall dry.

You can use a wide blade putty knife hold it at a low angle and heat gun and scraping sections at a time until you have removed it

Personally, I would blue grit, then re-skim

You can rub it down with sandpaper to take the sheen off then apply an oil based undercoat over it. This will then allow you to emulsion over the top

Sand it to give it a key. Prime with something like Zinsser Bullseye 123 which is a high adhesion primer. Finish with a couple of coats of whatever emulsion you like. No need to use oil based undercoat these days - it's not good for you and the Zinsser will do a better job anyway. And please don't be using a heat gun on plasterboard - it's a fire risk and you'll end up digging chunks out of the plasterboard.

There is no such thing as gloss satin wood. It's either gloss or satinwood