Thanks to Micah F Lee for the tip!
psql -d mastodon_production
mastodon_production=> UPDATE accounts SET created_at='1993-03-10 00:00:00' WHERE username='yawnbox';
Please note two things:
- The change is immediate. No need to restart postgresql.
- Set the day (“10” in the above example) ahead by one day. So you if you want March 09, 1993, set it to 1993-03-10.