Are you sure it is not just a rotary control, i.e. to the electrnics
world a potentiometer. Has it a screwdriver slot in the top? If so
small screwdriver and gently turn.

No. It is a little yellow dot that doubles as the pointer for the
temperature control. I suspect is has a protruding lug that prevents the
pointer being turned past 75C. By reversing the dot, I suspect the alleged
lug will no longer prevent the pointer being turned. The slot is in the edge
of the insert supposedly to give something for your screwdriver to grip on
when prising it out. It's a weird concept anyway, especially as there is a
software setting to limit the temperature as well. Both have to be set to
get 75C water.

Christian.