I've been trying to recreate this, feedback would be immensely helpful in ironing out any variations on bugs.
To find posts with duplicate likes you'd want to run the query:
SELECT
`POST_ID`, COUNT(`POST_ID`),
`USER_ID`, COUNT(`USER_ID`)
FROM
`ubbt_LIKES`
GROUP BY
`POST_ID`,
`USER_ID`
HAVING
COUNT(`POST_ID`) > 1
AND COUNT(`USER_ID`) > 1;
Then to remove those likes you'd want to:
DELETE FROM
`ubbt_LIKES`
WHERE
`POST_ID`='postidnumber'
AND `USER_ID`='useridnumber'
Where the postidnumber and useridnumber would be from the previous query.
ubbt_ in both queries would be whatever your database prefix is set to, default being ubbt_