We moved to using Git and PRs... then we moved to Azure DevOps from on-premise TFS.
Our developers still have a number of old, irrelevant code reviews in their Assigned to me section.
I tried following the directions here How can you cancel a Code Review Request? but using that method I was unable to set the Closed Status field. The edits would not save.
That's when I stumbled across a UI feature to simply Edit the items in the query.
Then we can set the State to Closed and the Closed Status to Abandoned.
Then click Save Items in the query menu, refresh the query, and they're all gone now.