You can rename attachments in bulk without downloading them by using the Rename Attachments with Airtable Field automation.
To set this up, simply follow the steps below:
Choose the table containing the attachments you want to rename.
Then select the field that contains the attachments that you want to rename.
Lastly, proceed to choose the field containing the desired name for the attachment (You can opt for any formula, long text, rich text, or single text field type).
When selecting the Prefix field to attachment name option, the content of the Airtable field (#3) will be inserted as a prefix to the existing name of the attachment.