How to retrieve deleted automated rds snapshots

I don't believe this is going to be possible, if the snapshot has a retention period of one day you won't be able to access snapshot from seven days ago.

If you want to have access to an automated snapshot for longer than its retention period you can copy it and store the copy as a manual snapshot (obviously before the automated snapshot expires and is deleted) https://repost.aws/knowledge-center/rds-automated-snapshot-retain-longer https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_CopySnapshot.html