How to repair an electronic igniter on a gas stove?
You didn't specify what is the failure mode of the unit..!! Did you changed its battery? Assuming its using battery, check for corrosion at battery holder/contacts.

High voltage spark points may have carbon or any other residue which might shorting out the arc. If its using piezoelectric generator (battery not used) very likely it may have shorted path in its high voltage side causing intermittent operations.

Electronic type using battery and boost converter. Any failure in this sections requires knowledge in electronics in order to repair it.