Access concealed wc cistern?

I have an armitage shanks cameo btw pan fitted into shades furniture with front panel removal. How do I access the cistern to fix slow filling and pathetic flush. I can remove the handle with an allen(?) key and release the front panel slightly but the handle mechanism is still attached and I cant seem to move the face plate but I daren't apply too much pressure. There is no access from above (fitted worktop). Any ideas please?