The following steps need to be taken to be able to delete archived redo logs that are no longer required by the CDC capture process:
1. Determine the new first_scn for your capture process

As per Oracle documentation: This query “determines a new first_scn value that is greater than the original first_scn value and less than or equal to the applied_scn and required_checkpoint_scn”. So the new first_scn is the lower value of applied_scn and required_checkpoint_scn.
2. Raise the first_scn for the change source:

3. Identify which redo log files can be deleted:

4. Write a script to delete or archive obsolete archived redo logs based on the results of the query in step 3.