You cannot roll back a transaction once it has commited. You will need to restore the data from backups, or use point-in-time recovery

What happens if we use rollback after commit?

After you commit the transaction, the changes are visible to other users’ statements that execute after the commit. You can roll back (undo) any changes made during the transaction with the ROLLBACK statement (see ROLLBACK.

Can I rollback to savepoint after commit?

The SQL SAVEPOINT statement can be embedded as static SQL in PL/SQL. For syntax details on the SQL SAVEPOINT statement, see Oracle Database SQL Reference. A simple rollback or commit erases all savepoints. When you roll back to a savepoint, any savepoints marked after that savepoint are erased.