Hi @Bec3168,
Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.
I suppose the best way to go about this depends on what your plans are.
If you intend to replace the whole external corner, you can use a flathead screwdriver or chisel to get underneath it and lever it up. You may need to pierce through the plaster a bit, but as you will need to patch it up after, this is not something you should stress about.
You can then grab the external corner with some pliers and forcefully pull the external corner out and away. They are attached with either Corner Bead Spray Adhesive, staples or a combination of the two so they are not too difficult to pull off. Some of the plaster compounds around the bead will also come off, but as you would be replacing it, this would need to be patched anyway so this isn't much of an issue.
If you would like to just replace the dented piece at the bottom, you can use an angle grinder with a cut-off wheel to cut the dented section out and peel it off in the same way as above. Once again, some damage to the surrounding plaster is to be expected, but you will need to patch it up regardless so there's no need to stress about this.
Once the small section is cut out, you can replace it with a small section of external corner bead ensuring the metal rib that creates the line of the corner lines up perfectly.
Check out How To Attach And Plaster An External Angle for a bit of extra guidance.
Whichever method you choose to use, as lacerations from metal are very common, please wear your gloves, eye protection, long work clothing and enclosed shoes as well as hearing protection if you are using an angle grinder.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
