Need to create static ip on egress

I need to assign a static ip on an egress gateway for out bound traffic, so that my third party can whitelist the static ip address to allow incoming traffic from my cluster. I am using KOPS in AWS. I might need to use a NAT Gateway too but I am not sure what is the best way to go and I need some advice. How do I define all outbound traffic uses either the egress or NAT Gateway, so that the third party sees the ip address associated with the traffic leaving my cluster. Thanks for helping.

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Cluster information:

Kubernetes version:
Cloud being used: (put bare-metal if not on a public cloud)
Installation method:
Host OS:
CNI and version:
CRI and version:

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