ForwardFor or ProxyPassReverse to externally resolve internal domain

So I have a set minio servers behind a firewall load balanced by an HAProxy. I’ve been testing traffic flow on a system “outside” the firewall - referred to here as “end user”.

There’s an ACL that points to backend minio, and backend definitions round robin to all the minio servers

The problem is: outside the firewall is and behind the firewall is

The “end user” browser puts in, which gets passed through the firewall, the Proxy hands the traffic off to the minio server which then returns the

The “end user” then sees: “” in the browser with times out or won’t resolve because “internal” doesn’t know about “external”

would a “ForwardFor” statement in the backend definition transpose the traffic back to “external” domain the end user can consume?
Or perhaps “ProxyPass/Reverse” do a header translation?
Am I on the right track?