l have a 306 and need to get rid of the 'spanner' symbol on the dash - the symbol which means it aint been serviced in ages???

l know taking the positive wire off the battery for 10 seconds, and putting it back on took care of my same issue. On my car now, turning on and off the headlights 3 times in succession clears some indicators as well. Or maybe??? Its telling you to service it, because there really is an issue?

go to a service shop or a dealer, you need a sophisticated computer to acomplish this

You have two choices -

Take it to a garage for servicing and they reset the cars computer.
or, go on an auction site and buy the gadget which plugs into your cars computer - and you may need a disc to go with it and reset it yourself. just make sure you service it too though! Ok?

Generally it is possible to reset the service indicator by holding the speedo trip button in and then turning on the ignition for ten seconds or so with the button still depressed. At least it is on a Vauxhall.
RoyS

hold down odometer reset button then turn on ignition the readout should then countdown from 10 to zero then show next service interval

Look on ebay, there are people who sell this information for a couple of quid.it worked on my Citroen Picasso a treat and l also had a Peugeot 206 which detailed how to do it in the owners manual. Have a look there first