How do I verify there is no XSS that was reported 3-years ago

[alpdog14]

I am completely new to this Bug Bounty and I need to understand how do I resolve this report bug bounty:

https://www.openbugbounty.org/reports/1203268/

This is no longer a bug at all, as we are completely redirecting all traffic. I have no idea how to actually resolve or report that there is no XSS issue. Please help me.