What can I use to forward a conection to port 3006 on the bastion to an RDS database?
It is possible on the Linux(Unix) bastion host.

Step-1: First ssh to the bastion host. eg. 16.23.14.20 is the bastion host.

# ssh root@16.23.14.20


Step-2: Create port tunneling by using the below command. eg. The RDS IP is 172.16.13.10

# ssh -L  3006:172.16.13.10:3006 localhost


Verify using netstat command.

netstat -ntulp | grep 3006


Note: If netstat command not available. Using sudo apt install -y net-tools or sudo yum install -y net-tools