This is the replacement flush valve from the newer RAK Compact toilets with the Geberit insides
Please look out for the reference number at the top of the valve (see images) to make sure that this is the correct valve for your toilet
If you get the correct valve you shouldn't need to do any plumbing! Simply remove the top part of the valve, leaving the bottom part fixed to the cistern tank. Simply line up the 'U' shaped grooves to see how (see images)
Then simply re-install the new one in the reverse manner, it's that easy
Dual flush push button also included. Part of your old button may still be attached to the cistern lid (see images)