If its just the odometer then its probably the bulb. If you have an srs pull the battery cable neg to disable the airbag.
Strong hand says you can wiggle your hand up from under the dash to change them. Great idea. If you know where they are go for it. If not you may need to pull the cluster. Remove the light switch knob and the dimmer knob. They pull straight off even if they don't seem like they do. My dim knob is always tight. Once off wiggle the little panel off and leave the fog light switch intact. You'll find 2 torx back there. If you have no accessories on the other side then yank the 2 square covers off the right side bewteen to cluster and the radio. They too pull straight off although you often have to pry one edge at a time. They clip on by little plastic tangs to the left and right of the cover. Be careful. Once off you'll see the 2 other torx. remove them and wiggle the cluster towards you and look for the 2 bulbs.
***Can someone help Cat_Brick here identift the bulbs. I forget where on the cluster they are and what colour base they have?***
--
91 Brick turning 400,000 this month