ELB Connection Draining

That will be configured on the Target Group under Attributes - Deregistration delay.

Source: https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-target-groups.html#deregistration-delay

I am referring ELB Connection Draining https://aws.amazon.com/blogs/aws/elb-connection-draining-remove-instances-from-service-with-care/

https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/config-conn-drain.html

The document you linked is for a Classic Load Balancer, which has been deprecated. If you are using a CLB, then the "Instances" tab will appear right below the tab name and you can edit the "Connection Draining" setting from there. If you're using a newer LB, then there is no "Instances" tab, however you can follow the link to the configured "Target Group(s)" where you'll find the "Deregistration Delay" setting as mentioned by zsewell on the "Attributes" tab.