InfoPath Dev

I have an access database and a form which is getting filled out by Engineers and emailed into the office. The form will be opened and a user will press submit to store the date. At the moment I have this set up, but the record cannot be added due to a record already existing (imported a list of records). What is the easiest way I can check if a record exists and then replacing it? I have programing knowledge and have looked around for ideas but to no avail. Help would be much appreciated.

How about changing your Submit to first Query the connection and look for the record. If it finds it, display a dialog box saying it already exists and stop processing rules. If not, it keeps processing and submits the new record?

OK, if it exists how would I go about overwriting the existing record?

If you query that record you should get an ID and if you use that with the submit, it should automatically overwrite.

Ok, I've quiered the table before submitting and the record is found (I've tested this with the use of a display message). However when it tries to submit I get the following error :

InfoPath cannot submit the form.
Some rules were not applied.
InfoPath cannot submit the form.
An error occurred while the form was being submitted.
The changes you requested to the table were not successful because they would create duplicate values in the index, primary key, or relationship. Change the data in the field or fields that contain duplicate data, remove the index, or redefine the index to permit duplicate entries and try again

 I have an ID key, sitePin(Primary key). Im using the sitePin to locate the record. I know this is caused because of the primary key not being able to change but not sure how to work around it.