Best way I found is if you can get access above board through loft, is glue/stick a piece of board above hole so it's overlapping hole all sides. Let it set. Then fill hole either with board and patch up hole joints with skim and fill out or again skrim tape around edges of hole and make good with filler or plaster, then re-cut hole.
If access not available you can still cut board to fit through hole and glue down a bit fidgitty but do able.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!