All tools honour a selection, this is basic GIS. So select your row first using the select by attribute tool then run the field calculate tool on the field you want to update. The update will only apply to the selection.
Be aware that if your initial selection fails, for example they have returned an incorrect serial number then when you run the calculate field tool it will overwrite everything as there is no selection and there is NO UNDO for that action.
You should not be exporting, editing and then importing that is simply inefficient.
Suggest you create some test data and explore this approach before you apply it to your operational data.