With that type, the push button(s) may pull out and then you can get to the plastic bolt that screws down into the flush valve, that's what holds the push button holder and therefore the cistern lid down.
That wasn’t a photo of mine. That’s what it should look like. In mine the white buttons are all stuck down. The white button is smooth and does not have a slot for screw driver. It just jammed down when I tried fiddling with screw driver
Ah ok, if the button holder won't unscrew on it's own (you may have to go a bit harder) then it may need to be broken out, that will probably mean a new flush valve.
You'll have to get the flush valve out of there then to get to the bits. You may be lucky and it's a bayonet/2 piece type ..... hold the body of the flush valve and twist it anti clockwise, if it twist a 1/4 odd turn and then stops then it should pull up. If it just keeps spinning around a nd around then there may be 2 taps near the bottom that need pushed in to release it from the base section.
If it doesn't move easily then it's a 1 piece and the cistern needs to be lifted off the pan to get to the securing nut underneath.
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