You'll need either the topic id or the post id that is being linked to. Depending on which you have, you can use one of the queries below, replacing 'topic_id' or 'post_id' with the number you have.

SQL Query
delete from ubbt_TOPICS where TOPIC_ID = 'topic_id'

or

SQL Query
delete from ubbt_TOPICS where POST_ID = 'post_id'

If you want to verify it's the right topic before deleting, you can change the query to:

SQL Query
select TOPIC_SUBJECT from ubbt_TOPICS where TOPIC_ID='topic_id'

or

SQL Query
select TOPIC_SUBJECT from ubbt_TOPICS where POST_ID='post_id'