How to turn radiator off?

not the screw, but that square handle base,
snug down the screw, then,
see if turning the square base, in either direction , get's you any movement,
then it's righty tighty, to close the valve,
if the valve stem is stiff,
go in a little, back out a little, go in a little more, back out,
rinse repeat,

second thoughts,
that fan system over the convector,
does that also turn on and blow heat ? where you don't want it ?
you might try disabling it,
either unplug that white connector on the left side,
or to the right, disconnect that sensor linkage holding sensor to the convector pipe,
lay the sensor on the floor and it won't heat up, and that should stop from switching on the fan also,

same affect as disconnecting white connector on left,