How to fix & price of fixing the trip counter?

G/f's motor is a '98 Polo L. When we bought it, it kept flashing up service & what not. Had it serviced & it was still flashing until it'd been started a couple mins or so - but then it went in for the mot & she said it doesn't display it any more.

Aside from that, the trip counter reset button has NEVER worked.

As i'm guessing this is due to some wiring/connection issue? How'd she go about getting this sorted & what would the likely fee be for it to be fixed? As if it's an expensive job, then it's hardly worth it.