Now the problem is, when pushing either of the two buttons, or both together, the water in the tank doesn't release to flush the toilet.I got the centre piece out:
I realized that the disk with the grey rubber ring, just falls off the centre piece that lifts up when the buttons are pushed on top. I imagine it should pull up the disk to release the water but it doesn't stick on there, it just pops right off.
I got it somewhat reassembled, but with a little vibration it falls right off, it just holds on there by friction.
It seems like some thing that holds it up may be missing...? Any hints? The assembly looks to be the same as this one from WaterMark: https://www.alibaba.com/product-detail/Watermark-Upc-Toilet-Htd-New-Wra_60870640816.html