Issue with Database Connect from K8s pod
Rule number 1 never make your database public. If you look in the logs, hackers are probably brute-forcing it right now.
The fact you are getting an AccessDenied, suggests the networking is correct, but something is wrong with the password you are supplying.
I would create a bastion in the same subnet as the k8s pod and connect to the database from there with the username and password.