this query might give you a starting point to remove the duplicates. Oracle has a concept called rowid. It gives all your records a unique identifier.
This rowid should typically not be used in any query (it is a relational database after all, we should never address a record this way), but it can help you in this occasion.
You have to find all records that have the same values in all columns (duplicates), and only keep one of them.
In my example, I have kept the one with the lowest rowid.
Ensure that you understand the concept before trying it.
Test first on a test database!
Make a backup!