To provide additional safeguards for encrypted data at Application Load Balancers (ALBs) through the use of a unique random session key, the network engineer should focus on ensuring that the encryption method supports forward secrecy (FS). Forward secrecy ensures that even if the private key of the server is compromised, it cannot be used to decrypt past communications, as a unique session key is used for each session. Option A, changing the ALB security policy to support TLS 1.2 protocol only, enhances security but does not specifically address the requirement for forward secrecy. Option B, using AWS KMS to encrypt session keys, is not directly related to implementing forward secrecy at the ALB level. Option C, associating an AWS WAF web ACL with the ALBs and creating a security rule to enforce forward secrecy, is not the correct approach as AWS WAF is used for web application firewall protections, not for configuring encryption protocols. Therefore, the correct action is Option D, changing the ALB security policy to a policy that supports forward secrecy (FS), as this directly meets the requirement by ensuring that each session uses a unique random session key.