How to configure AWS load balancer to forward to external IP address
AWS Application Load Balancer’s Target Group can have either EC2 instance or IP address targets. In your case you need to use the IP address targets.
Here are the instructions: Application Load Balancing to IP Address
These addresses can be in the same VPC as the ALB, a peer VPC in the same region, on an EC2 instance connected to a VPC by way of ClassicLink, or on on-premises resources at the other end of a VPN connection or AWS Direct Connect connection.