You need to be more clear when writing your question. Please include the code that you are working with and a detailed explaination of why it isn't working. Include error messages that you get.
In general, it sounds like you want to search a database for a key value, then update a quanitity value. This is a very common task and you can probably find a lot of articles about how it's done by googling or looking at articles here on Code Project. The only difficulty that I can see is that you are coding in VB6. Is this a strict requirement? VB6 is an old language. If you have the choice, you really should look into VB.Net. Visual Studio Express is a free version of the IDE. You'll find a lot more documentation and articles to help you with a newer language.
Here[
^] are some google results for vb6 data access tutorials that may help guide you.