Hi @needhelp123,
A warm welcome to the Bunnings Workshop community, it is wonderful to have you with us.
You'll want to start by turning off the water supply and draining the cistern. There should be a stop cock connected to that braided hose that can be turned off. Once the tap is closed, flush the toilet to drain the water, then use a towel to dry up the remaining water.
Once drained, the flush valve will be either a twist-lock or a nut-fixed system. If you've turned it and it is still stuck in place, look for clips on the side of the valve. These clips may need to be pushed in to free it up and allow removal. If you can't locate any clips, look for a nut at the base of the valve. If you can see one, undo the nut and try to remove the valve.
If you still have no luck, please upload some photos showing the sides and bottom of the flushing valve so we can assist further.
You might also like to check out How to fix a leaking toilet.
Jacob
