Datalinks and inserting between DBs

Hi, I've already set up a database link between my two databases.

I am now trying to insert 1 record from a table on database a into the same named table on database b. Records already exist on database b though so I only want to insert one new record and not delete any existing ones.

I'm struggling to get it right though. Can someone review what I've suggested below?

insert into destinationdb tablename
select * from sourcedb tablename
where customernumber = 'ABC';