You can use our Create Records in Bulk from CSV File automation for this. It processes CSV files stored in attachment fields (e.g. uploaded through a form or portal) and will generate and/or update records in a target table based on the data within. It functions in a similar way as our regular CSV Importer automation, but with CSV files sourced from an attachment field, instead of a link.
The Unique ID Field Name (for Upsert) setting is required, as it is crucial in identifying existing records. Without it, the automation would have no way of knowing which record to update with what data.