Update row with multiple row in another table Error : ORA-01427: single-row subquery returns more than one row?
Community wiki answer:

Since there are several rows in the result you need to decide which one to use as the new value for trn_status: 


Limit your subquery with FETCH FIRST 1 ROW ONLY.
If you can guarantee that all corresponding records are full duplicates, use DISTINCT.
Using min, max, avg aggregate would be other possibilities.