Access to inlet valve on Vista cistern to change it ?

The unit is against the bathroom wall, and the cistern sits on the main part of the toilet. The only screws are to hold the cistern to the wall and two in the base of the cistern. There are screws on the side of the toilet bowl at the side.

The supply pipe which is in a void the other side of the bathroom wall just disappears through the wall with no means of disconnecting it

Any help appreciated