Hi there, I'm in Australia and have the equivalent vehicle, a Honda Euro.
You can adjust the outside temperature reading up to minus or plus 3
degrees, but your temperature must be slable when doing it.
The way to alter the temperature is to select the outside temp display, then
press the the select/reset knob for 10 seconds. The following sequence will
appear for one second each: 0, 1, 2, 3, -3, -2, -1, 0.
When it reaches the value you want release the Select/Reset knob.
You should then have the temperature you want.
Hope that explanation makes sense.

Cheers
Roy