It seems you are trying to add HTTP headers. You can use both local traffic policies or irules to achieve this. For more information about local traffic policies see:
https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/local-traffic-policies-getting-started-12-1-0/1.html
Below you'll find an example of an iRule:
when HTTP_REQUEST {
HTTP::header insert X-Forwarded-For [IP::remote_addr]
}
This article could also be useful. It compares BIG-IP LTM and NGINX configurations:
https://www.nginx.com/resources/deployment-guides/migrating-load-balancer-configuration-f5-nginx-plus/