Urgh! I mailed wrong queue
find transaction number of comment you want to change
eg: /rt/Ticket/Display.html?id=1334#txn‑15624
check if ticket number matches and update it
rt4=# select * from transactions where id = 15624 ;
-[ RECORD 1 ]-+---------------------------------------------------------------
id            | 15624
objectid      | 1334

update objectid
(which is really ticket number)
rt4=# begin ;
BEGIN
rt4=# update transactions set objectid= 1290 where id = 15624 ;
UPDATE 1
rt4=# commit ;
COMMIT