Thanks for reaching Microsoft Q&A.
Regarding your question is much more specific to RDS AWS service. However, try to check this link if it helps you.
https://stackoverflow.com/questions/56254948/allow-aws-rds-connection-from-an-azure-k8s-pods
https://www.strongdm.com/connect/amazon-rds-aks
Hope this helps. Please "Accept as Answer" if it helped, so that it can help others in the community looking for help on similar topics.