Hi @FeatherBlue,
A warm welcome to the Bunnings Workshop community and thank you for your question.
What you are looking at is an expansion anchor similar to this Ramset 10 x 50mm DynaBolt Plus Hex Nut Bolt.
The sleeve around the bolt expands outwards as the nut is tightened, pulling the bolt up through the expansion sleeve.
Sometimes, you can reverse this expansion by forcing the bolt back through the sleeve using a hammer and a nail punch with a wide head, such as this Trojan 5mm Nail Punch.
Place the tip of the nail punch on the central bolt and hit it back down through the sleeve and into the wall.
If you're able to get the bolt to move and the expansion sleeve stays in place, you can then use some pliers to grasp the expansion sleeve and pull the Dynabolt out of the wall.
Unfortunately, this method doesn't always work, in which case you would have two options.
Either drive the Dynabolt down below the surface of the wall and cover it with a suitable filler or use a drill to drill out the bolt and pull the sleeve out.
Let me know what you think, and if you have any further questions, please don't hesitate to ask.
Jacob
