howto setup an IP whitelist for on a port monitored?

[Emmam]

I have a External Network (Passthrough) Load Balancer. I want to setup an IP whitelist for on a port monitored to restrict access. I don't know how to setup, for example port 7687 in the picture.

I tried to enable traffic steering in the frontend configuration, but it doesn't seem to be the effect I wanted to achieve.

Does anyone know ？