1989 Chrysler Le Baron Odometer does not increase

Computer problem
1989 Chrysler Le Baron 4 cyl Automatic 95500 miles

I bought this 89 Le Baron about 2 weeks ago. It runs great and looks new. I've noticed after I got my oil change that the odometer was not increasing, however the speedometer and all other meters are working just fine.

Is this fixable? If so, is it something a person with a set of tools can do, or should it be left to a certified mechanic, or mechanic chain (Pepboys, Firestone, etc)

If not fixable, what action should I take?

I purchased the car from a private owner for $1800.