Merging records when new record created matches the primary field in Automations

Hi there!

We have a form which asks users to give feedback. They all already have a “master record” with more information. When new records are created with this, I’m trying to create an automation which finds the “master record” and adds in the new fields to it.

I can’t replace the record, and know that I could do this with Dedupe but it’s simply not scalable. The form is also an airtable form, so ideally wouldnt have to get e.g. Zapier involved. Currently I’m thinking an automation with an appropriate script? I can’t get ‘Update Records’ to work for this use case as an Automation, as two records I want to merge have different IDs.

Would LOVE any help. Thanks!