Welcome to the community, @Mely! :grinning_face_with_big_eyes: This can be done via automation, but doing so will require a script action, which is only an option if your base is in a Pro-plan workspace or higher. In short, the automation would trigger on a new record appearing in [Table A]. The script would run, read the customer ID from that new record, then search for that ID in [Table B]. If found, it would update the [Table B] record. If not, it would just exit without doing anything.
Eventually the hope is that Airtable will add support to automations for conditional logic, which would mean that this could be done without a script. Until that happens, scripting is the only method I’m aware of that would allow this to work cleanly.
If you’d like help with the script and have a budget for hiring a developer to write it, message me and we can discuss the details.