Self-answer:
1) kill chatty
2) sqlite3 ~/.purple/chatty/db/chatty-history.db
3) find necessary thread_id:
select * from threads where name like "%username%" limit 10;
4) find target message(s):
select * from messages where thread_id is NUM and time >= SECONDS limit 20;
NUM from 3)
SECONDS is in date "+%s", e.g. for recent day.
5) delete necessary message(s):
delete from messages where id = ID;
ID is from 4) output
6) run chatty again (e.g. by running gui app)
1) kill chatty
2) sqlite3 ~/.purple/chatty/db/chatty-history.db
3) find necessary thread_id:
select * from threads where name like "%username%" limit 10;
4) find target message(s):
select * from messages where thread_id is NUM and time >= SECONDS limit 20;
NUM from 3)
SECONDS is in date "+%s", e.g. for recent day.
5) delete necessary message(s):
delete from messages where id = ID;
ID is from 4) output
6) run chatty again (e.g. by running gui app)