Okay then, put this in a psql console:
discourse=# UPDATE posts
SET hidden = false, hidden_reason_id = NULL, hidden_at = NULL
WHERE user_id = (SELECT id FROM users WHERE username_lower = 'fhtzoob')
;
UPDATE 5000
discourse=# \q
Or, from a Rails console: (./launcher enter app then rails c)
ActiveRecord::Base.exec_sql("UPDATE posts
SET hidden = false, hidden_reason_id = NULL, hidden_at = NULL
WHERE user_id = ?", User.find_by_username("fthzoob").id)